


LIBRARY OF CONGRESS 


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UNITED STATES OF AMERICA 


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THE 


Constructive Materials 


OF 


ENGINEERING 



0 


BY 

Albert W. Smith 

w 

Professor of Mechanical Engineering, Leland Stanford Junior University 



Palo Alto Press: 

Leland Stanford Junior University 
1892 





4 


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Copyright, 1892, by ALBERT W. SMITH 




The work of tire following pages is the outgrowth of lectures 
before the students in Mechanical Engineering at Cornell University, 
the University of Wisconsin, and Leland Stanford Junior University. 

The object of the work is to give the student a start toward that 
understanding which shall enable him to select materials best 
adapted for machine parts subjected to different working conditions. 

An effort has been made to omit all unessential details, and to 
treat of underlying principles only. The treatment of metallurgical 
processes' for the production of iron and steel is only the barest out¬ 
line ; and is given chiefly as a help toward better understanding of 
what follows. 

The books which have been freely consulted for this work are 
given in the bibliography appended. To the authors of these books 
I here offer grateful acknowledgement. A. W. S. 

Palo Alto, November, 1892. 




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CONTENTS 


PAGE 

Outline of the Metallurgy of Iron and Steel, - - - - L 

Representation and Interpretation of the Physical Qualities of 

Materials, --------26 


Variations of the Physical Qualities 
and Control, - 

Variations of the Physical Qualities 
Causes and Control, 

Alloys, - - - 

Selection of Materials, - 

Bibliography, - 

Index, - 


of Cast Iron, Their Causes 

_31 

4 

of Forged Materials, Their 

45 

. 62 * 
67 
- 75 
77 




CHAPTER I. 


Outline op the Metallurgy of Iron and Steel. 

1. Fuels.—A high temperature is necessary for most metallurgi¬ 
cal processes, and it is usually obtained as a result of the heat 
evolved by the chemical combination of the oxygen of the air with 
some oxidizahle substance. The latter is called fuel. 

Fuels are solid, liquid and gaseous. Petroleum is the only 
liquid fuel of any importance. It is used often in re-heating fur¬ 
naces, but will not be considered here. 

Solid fuels are vegetable in their origin and consist chiefly of 
carbon, hydrogen, and oxygen, with a small amount of earthy 
matter which remains as a residue after combustion and is called 
ash. Carbon and hydrogen are the oxidizahle constituents, and on 
these the value of the fuel depends. When hydrogen and oxygen 
are present in fuel the only part of the hydrogen that is useful for 
generation of heat is that which is in excess of the amount neces¬ 
sary to unite with the oxygen present for the formation of water, 
because the hydrogen and oxygen are already in chemical com¬ 
bination. 

Complete Combustion of an element is the combination with such 
an amount of oxygen as shall produce the most stable compound. 
Thus the complete combustion of carbon is its combination with as 
much oxygen as is required to produce C0 2 ; and the complete com¬ 
bustion of hydrogen is its combination with as much oxygen as is 
required to produce H 2 0. 

The complete combustion of one pound of any combustible 
always produces a definite amount of heat, and this amount is 



METALLURGY OF IRON AND STEEL. 


2 


called the calorific power of the combustible. It is expressed in 
British thermal units. 

Definition.—A British Thermal Unit is the quantity of heat necessary to 
raise the temperature of one pound of water one degree Fahrenheit, 
at the temperature of maximum density. The value of the calorific 
power has been experimentally determined for different combust¬ 
ibles. If a combustible or fuel be burned completely in air, the heat 
evolved will produce, a certain temperature in the gaseous products 
of the combustion. This temperature (in degrees Fahrenheit) is the 
calorific intensity of the fuel. 

Let it be required to determine the calorific intensity of pure 
carbon. The combustion is represented thus: 

12 32 44 

c+o 2 =co 2 

The molecular weights are written above the symbols. It will 
be seen that for every 12 units of carbon, 32 units of oxygen must 

32 

be supplied, and for every one unit of carbon, — units oxygen must 

1 A 


be supplied. But the oxygen is supplied from the atmospheric air; 
and this is composed, by weight, of nitrogen 0.77, oxygen 0.23. 
Hence for every 23 parts of oxygen supplied, 100 parts of air must 

be supplied ; and for every one part of oxygen, parts of air must 

Ao 


be supplied. Therefore for the complete combustion of one pound 
of pure carbon, the amount of air to be supplied =11.6 


lbs. The products of combustion are nitrogen and C0 2 . The nitro¬ 
gen is inert as far as combustion is concerned; its amount = 0.77 of 
the air supplied 11.0X0.77 8.93 lbs. For every pound of carbon 

44 

there results —=3.66 lbs C0 2 . 

J A 

Experiment shows that for every pound of carbon burned there 
will be evolved 14,500 B.T.U. This amount of heat is therefore 
available to raise the temperature of 8.93 lbs nitrogen and 3.66 lbs C0 2 , 
and the resulting temperature (= t) is required. The specific heat 












METALLURGY OF IRON AND STEEL. 


3 


of nitrogen = 0.244, and of C0 2 —- 0.2164, and hence for every degree 
that 8.93 lbs nitrogen is heated, there are used 8.93X0.244 B.T.U., 
and to heat it to the temperature t, 8.93X0.244Xt B.T.U. are 
used. Similarly to heat 3.66 lbs C0 2 to t, 3.66X0.2164Xt B.T.U. 
are used. But the amount of heat that raised the temperature 
of both to t, is 14,500 B.T.U. Therefore t(8.93X0.244+3.66 X 
0.2164) = 14,500, hence t—4872° F., the calorific intensity of 
pure carbon. 

The theoretical temperature thus found is never attained, be¬ 
cause (a) combustion is seldom complete ; (b) an excess of air is 
always supplied; (c) the fuel is never entirely consumed; (d) there 
are always radiation losses; and (e) the moisture usually present in 
the fuel absorbs heat, in being vaporized and raised in tempera¬ 
ture. 

2. Solid Fuels may be classified as: 

a. Raw Fuels, as wood or coal. 

b. Artificial Fuels, as charcoal or coke. 

Wood is composed of cellulose, water, and ash. Cellulose con¬ 
sists of carbon, 44.44 per cent; hydrogen, 6.07 per cent; oxygen, 
49.39 per cent.; or C 12 H 20 O 10 . It will be. seen that hydrogen and 
oxygen are present in the proper proportions to form water, and 
therefore no hydrogen is available for combustion, and the carbon, 
which is alone available, is less than half the weight of the fuel; 
also, the calorific intensity is reduced by the water present. Wood 
cannot be used directly, therefore, for the production of very high 
temperatures. 

Coal is often classified as follows: 


Coal l 



Vegetable matter is really converted into coal by gradual 
change, and so each division of the classification covers a wide 
range, and blends into the others. Description of coals is unnec¬ 
essary. 





METALLURGY OF IRON AND STEEL. 


4 


Average values per cent, of the constituents of coals are as 
follows (exclusive of ash): 



Carbon. 

H and O (proportion, 
to form water.) 

H available for 
combustion. 

Lignite 

65 

33 

2.0 

Bituminous 

78 

19 

2.8 

Atnhracite 

94 

4 

2.4 


From this it appears that as the change progresses from veg¬ 
etable fibre to anthracite coal, the percentage of combustible, and 
therefore the calorific intensity of the fuel, constantly increases. 

It has been explained that wood has a low calorific intensity, 
because of the presence of a large amount of hydrogen and oxygen, 
which are present in proportion to form water; the hydrogen being 
therefore unavailable for the production of heat. If wood be heated 
between the limits 300° F. and 750° F., and with partial exclusion 
of air, the hydrogen and oxygen pass off as gas and vapor, and 
very nearly pure carbon is left, which is called charcoal. Its calor¬ 
ific intensity evidently nearly equals that of pure carbon. 

If bituminous coal be heated with partial exclusion of air, its 
volatile constituents are driven off, and coke remains, consisting of 
nearly pure carbon. 

The calorific power of C burned to C0 2 =14,500 B.T.U. 

“ “ “ “ “ “ CO -40,174 “ 

Therefore “ “ “ CO “ “ C0 2 ^ 4,326 “ 

But the calorific intensity of C burned to CO,=4872° F., while 
the calorific intensity of CO to C0 2 is about 5400° F. That is, al¬ 
though carbon by complete combustion evolves 14,500 B.T.U. per 
lb, and CO only 4326 B.T.U., yet the resulting temperature in the 
second case is higher than in the first. The combustion of CO oc¬ 
curs as shown by the following formula: 

28 16 44 

co+o=co 2 

Therefore for every 28 parts of CO, 16 parts of oxygen must be 
supplied; or for every part of CO, ^ parts of oxygen must be sup¬ 
plied; and for every part of oxygen, parts of air are required. 














METALLURGY OF IRON AND STEEL. 


Therefore, for every pound of CO, ^ x t|+^ 2 - 48 pounds of air 

are required. Of this air 0.77= nitrogen = 1.9 lbs. Also the CO, 
44 

produced equals ^=1.57 lbs. The products of combustion there¬ 


fore are nitrogen 1.9 lbs ; C0 2 1.57 lbs. To raise the temper¬ 
ature of these gases, 4326 B.T.U. are available. Hence, 

t - 4326 __ 4828 , 400 o F 

(1.9X0.244)+(1.57X0.2164) .803 

In the case of carbon burned to C0 2 it was seen that 14,500 B.T.U. 
were available to raise the temperature of 8.93 lbs nitrogen and 
3.66 lbs C0 2 . The reason for the higher calorific intensity of CO is, 
therefore, that while the available heat is less, the weight of gases 
to be heated is less in very much greater degree. 

The calorific 'power of hydrogen is 62,000 B.T.U., while the 
calorific intensity is only 3250° F., much less than that of carbon. The 
reason for this is the greater relative weight of the products of com¬ 
bustion, their greater capacity for heat , and also, the water formed 
has to be vaporized, with the absorption of 966 B.T.U. per pound, 
which have no effect to raise temperature. 

3.—Gaseous Fuel has a number of advantages over solid fuel for 
some of the metallurgical processes. 

1st. Inferior solid fuel may be used for the generation of the 
gas fuel. 

2d. The furnace for production of the gas may be at some dis¬ 
tance from the furnace where the gas is used ; the transfer being 
made by means of pipes. Valuable space is thereby sometimes 
saved. 

3d. It is much easier to apply heat uniformly over a given sur¬ 
face, or to concentrate it locally, with gaseous fuel than with solid 
fuel. 

4th. Mixture of the air which supports combustion with the 
fuel can be much more complete, and therefore the excess of air 
over that absolutely necessary for complete combustion is reduced 
to a minimum, and a gain in calorific intensity results. 




METALLURGY OF IRON AND STEEL. 


6 


5th. If the mixture of air and gas be properly regulated, there 
will be complete absence of smoke and soot, and the latter will not 
be mixed with the material treated. 

There are three methods for the production of gaseous fuel from 
solid fuel : 

1st. Dry distillation in retorts, of coal, containing a large per¬ 
centage of volatile constituents. This process is similar to that for 
the production of coke, except that here gas is the product and coke 
the by-product. The gas produced is illuminating gas. Its com¬ 
position is variable, hut usually about as follows: 

H 40 to 50 per cent, by volume. 

CH 4 30 to 40 
CO 8 to 14 

There are usually also small amounts of CH 4 , nitrogen, oxygen, 
C0 2 , and vapor of water. 

2d. Another method is to pass steam over incandescent carbon. 
The product is known as “ water gas.” The reactions are as follows : 

C -|- 2 H.,0 ~C 0 2 -f 411. 

C0 2 +C =2CO. 

CO -f H 2 0 —C0 2 +2H. 

These reactions probably go on simultaneously, and when the 
process is properly regulated the gas is about of the following com¬ 
position : 

. C0 2 2 to 15 per cent, by volume. 

CO 20 to 40 “ 

H 50 to 65 “ 

CH 4 4 to 8 

C 2 H 4 , etc 0 to 6 “ “ 

When this gas is used for illumination it is passed through a 
second furnace, where it comes in contact with vapors of petroleum 
or naphthalin, and so is enriched with hydro-carbons. 

3d. This process is most important to the metallurgist, and 
consists of burning coal with incomplete air supply. 

The generator consists of a chamber, A, (Fig. 1) lined with fire 







METALLURGY OF IRON AND STEEL. 


7 


brick. One side of this chamber, B, slopes at an angle of from 45° 
to 60°, and at the bottom joins a grate, C. Fuel slides down 
the inclined side, having been introduced through a hopper, D, 
which has two doors so that communication with the air need not 
be made when the solid fuel is put in. Air is admitted through^ 
the grate, and the pipe, E, brings water which is admitted to the 
ash pit in small quantities. The chamber is connected to the gas 
flue by the passage F. The most rapid combustion occurs near the 
gfate. The action is as follows : Air passes through the grate and 
combines with the incandescent carbon, forming C0 2 ; this passes on 
up and comes in contact with more incandescent carbon, where the 
oxygen supply is small, and takes up more carbon and becomes 
CO, passing up into the chamber. In the upper part of the coal, 
where the heat is less intense, the volatile constituents distil off. 
In fact the action is the same as in the illuminating gas retorts, 
with the production of hydrogen, CH 4 , etc. 

This, of course, leaves coke, which descends slowly, becoming in¬ 
candescent, and uniting with the oxygen and C0 2 to form CO. Also 
the water, in the form of vapor, passes through the grates with 
just the same result as in the manufacture of water gas, viz: the 
production of hydrogen and CO. Water has an advantage over 
air, in that it carries no inert nitrogen to absorb heat, but it has 
high capacity for absorbing heat, and if it be admitted in too 
large quantities it reduces the temperature in the furnace. 

An average of the resulting gases from this process is as follows: 



( CO 

24.2 per cent, by volume 

Combustible 

] H 

8.2 


( OH, 

2.2 “ “ 

Incombustible 

\ co . 2 

N 

4.2 “ “ 

61.2 


4.—It is seen that 34.6 per cent, is combustible, w r hile 65.4 per 
cent, is incombustible, and therefore that this must be a fuel of low 
calorific intensity. It would seem, therefore, that “generator gas” 
could not be used for producing high temperatures. It becomes 














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METALLURGY OE IRON AND STEEL. 


8 


available, however, for this purpose through the Siemens Regenerative 
Furnace, the invention of Messrs. Frederick and C. W. Siemens. The 
gas, instead of being admitted to the furnace directly, passes through 
a chamber, A, (Fig. 2) filled with “chequer work,” i. e., full of small 
intricate passages, surrounded by refractory material that is suitable 
for absorption of heat. The air also passes through a similar 
chamber, B, and meets the gas at C, the entrance to the hearth, H, 
where the metal is treated. The air is admitted above the gas, so 
that, because of its greater specific gravity, it shall mix more com¬ 
pletely with the gas. Combustion occurs at C, and the products of 
the combustion, heated to a temperature corresponding to the calor¬ 
ific intensity of the fuel, pass over the hearth and through the 
chambers A' and B' to the stack. In doing so they heat up the 
chequer work of the chambers A' and B' to their own temperature, 
if the process be sufficiently long continued. Then the connections 
are changed so that the gas comes in through A' and the air supply 
through B', and A and B are connected with the stack. Now the 
gas and air passing through the heated chambers have their temp¬ 
eratures raised before combustion takes place ; then the temperature 
is still further raised by the combustion, so that the products of 
combustion now pass to the stack through A and B until the chequer 
work of their chambers is raised to this higher temperature, when 
the connections are again reversed and the gas and air are heated to 
this higher temperature before combustion, and so on. It would 
seem that there would be no limit to the temperature that could be 
produced in this way. But a point is reached after a while where 
the temperature is so high that dissociation or breaking up of CO 
and C0. 2 occurs, and there can be. no further combination of C and 
O at this temperature with evolution of heat. 

5.—Furnaces used for the heating, fusion, or reduction of metals or 
ores, may now he classified as follows : 

1st. In which the metal or ore, either in crucibles or not, is put 
into the same chamber with solid fuel, and in this chamber both com¬ 
bustion of fuel and reduction or fusion of metal or ore takes place. An 
example of this type of furnace applied to fusion is the ordinary 


































































































































METALLURGY OF IRON AND STEEL. 9 

foundry cupola ; applied to reduction, the blast furnace stack. Brass 
furnaces, and some steel furnaces for fusion, are also of this class. 

2d. In which gaseous fuel is generated in a separate furnace, 
and conducted in pipes to the furnace in which the ore or metal is 
treated. The Siemens generator combined with the regenerative 
furnace is an example of this ; also furnaces in which natural or 
illuminating gas is used. 

3d. In which the fuel is gaseous, but is generated in a fire 
box which adjoins the treating chamber, and is separated from it 
by a “ bridge wall.” The reverberatory furnace, which is an example 
of this, requires description. See Fig. 3. 

A is a fire box having a grate on which solid fuel is charged, 
and burned chiefly to CO. An opening above the fire serves to 
admit air, which combines with the combustible gases coming from 
the somewhat restricted combustion of the solid fuel, and a long 
flame passes over the bridge wall, and strikes the downward slop¬ 
ing top wall of the furnace and is deflected on its way to the stack, 
C, so that it heats anything which may be in the hearth, B. 

This type of furnace is used for a great variety of metallurgical 
work. It will be seen that in this furnace, as well as in the fur¬ 
nace in which the fuel and metal are “ charged on ” together, the 
highest attainable temperature is dependent upon the calorific in¬ 
tensity of the fuel used; whereas in the second class, in which the ef¬ 
fect is cumulative, any temperature below that of dissociation of CO 
may be attained. 

6.—Sources of Iron. Iron is obtained almost exclusively from 
oxides. Carbonates are also smelted, but by preliminary treat¬ 
ment they are reduced to oxides, by the driving off of C0 2 . 

Full consideration of the ores of iron is beyond the scope of this 
work, but a few of the most common will be briefly described. 

Magnetite, or magnetic iron ore, is an oxide represented chemically 
thus: Fe 3 0 4 . It is black or dark brown in color, and is usually 
crystalline. When pure it sometimes yields 72 per cent. iron. 
Nearly all Swedish iron is made from this ore, and it occurs in 
large quantities in Norway, Sweden, Russia, and North America. 


































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METALLURGY OF IRON AND STEEL. 


10 


The oxide Fe 2 0 3 occurs chiefly as Eed Haematite. This ore has a 
rich, red color, is granular (sometimes crystalline or fibrous), and 
often contains small fossils. When pure it contains about 70 per 
cent. iron. Other varieties of this ore have special names, as 
specular ore , kidney ore , etc. Haematite is much more widely 
distributed than magnetite. 

Franklinite is an ore found in New Jersey which consists of oxides 
of zinc, manganese and iron, Fe 3 0 4 . It is first smelted for the zinc, 
and then the residue is smelted for u spiegel eisen,” which is a com¬ 
pound of iron, carbon, and manganese. The use of spiegel eisen will 
appear later. 

Brown Haematite is Fe 2 0 3 with chemically combined water, i,e., it 
is a hydrated red haematite. 

Bog ores are impure brown haematites. 

Spathic ore, Siderite, Olay Ironstone, and Blackband, are all names for 
different forms of carbonate ores ; i.e., FeC0 3 combined with dif¬ 
ferent amounts of other substances. The carbonate ores are the 
chief source of iron in England. 

Beside iron oxide, ores contain varying amounts of water, H 2 0; 
carbonic acid, C0 2 ; sulphur, S; arsenic, As; silica, Si0 2 ; alumina, 
A1A ; lime, CaO ; magnesia, MgO : and some other impurities of less 
importance. The first four may be removed as vapor or gas at com¬ 
paratively low temperatures, and this is the object of the process of 
calcining or roasting. The others are removed by other means, to 
be explained later. 

7.—For Calcining or Boasting the ore is piled in heaps out of doors 
or in kilns, with fuel in proper amount mixed with it. The fuel is 
ignited, the mass is slowly heated up. Water is driven off as steam. 
If the ore is carbonate, FeC0 3 , the C0 2 is driven off, and the result¬ 
ing FeO is changed to Fe 2 0 3 by combination with oxygen of the 
air. If any iron pyrites, FeS 2 , is present the sulphur is oxidized, 
passing off as S0 2 (gas), while the iron is also oxidized, remaining as 
Fe 2 0 3 (solid). Arsenic is oxidized if present. By the process of 
roasting the structure of the ore is made more open, and hence better 
fitted for smelting. 




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METALLURGY OE IRON AND STEEL. 


11 


When roasting is carried on in kilns it is often a continuous 
process. The kiln is like a foundry cupola, much enlarged in 
diameter; the ore and fuel are charged in at the top, and the roasted 
or calcined ore is withdrawn from openings at the bottom. 

8.—All of the early methods for the production of iron were direct 
methods, i.e., the product was wrought iron, which had not passed 
through the intermediate state of cast iron. 

Chemically this process is as follows : Rich ore, Fe 2 0 3 or Fe 3 0 4 , 
is charged with charcoal into a rectangular hearth, and artificial 
blast is supplied. The coal is ignited and the oxygen of the air 
combines with the carbon of the fuel to form C0 2 , which passing 
on over more incandescent carbon is reduced to CO, which comes in 
contact with the Fe 2 0 3 , when the following reactions take place : 

3 Fe 2 0 3 + CO=2 FeA+C0 2 
2 Fe.A+2 CO—6 FeO +2C0 2 
6 FeO +6 CO=3 Fe 2 +600* 

Metallic iron and C0 2 are therefore produced. But the ore also 
contains some silica, alumina, etc., which is very infusible, and which 
must be rendered fluid for removal from the iron. It happens that 
silicia and alumina unite with FeO to form a “ slag ” which is fusible 
at a low temperature. Some of the FeO which is produced by the 
process (see above reactions) acts as a “flux” i.e., renders fluid the 
earthy matter, separating it as fluid slag, which may be partly 
drawn off, while the iron remains in the hearth, a spongy mass filled 
with molten slag. This mass is heated to a welding temperature 
and taken to a hammer or squeezer where the slag is removed, and 
the mass is welded into a bloom. 

The details of the carrying out of this process vary. It re¬ 
quires rich ore, charcoal for fuel, and the waste of iron in the slag 
is very great. It is therefore a very expensive process, and is not 
available for the production of large quantities of iron. 

9.—Nearly all the iron used today is reduced from ore to pig iron 
in the Blast Furnace. Fig. 4 shows the outline form in section of a 
blast furnace. The height varies from 40 to 100 feet, and the diam- 



METALLURGY OF IRON AND STEEL. 


12 


eter at the “ boshes ” varies from 12 to 25 feet. The form of outline 
varies with the kind of ore and fuel used, and with the pressure and 
amount of the blast. 

Air is supplied, under pressure, to the large pipe CC, which 
surrounds the stack, and at intervals of the circumference smaller 
pipes convey the air to the tuyeres TT, which deliver it into the 
furnace. 

The action of the furnace is continuous, solid materials, ore, 
fuel, and flux being introduced into the top of the stack, and liqui¬ 
fied pig iron and “ slag ” being drawn off from the bottom. 

The “ bell,” B, prevents the escape of gas from the top of the 
stack, and insures its delivery into the gas main. The solid ma¬ 
terials to be “ charged on ” are placed in the annular space, A A, and 
the hell is lowered by power; the charge drops into the furnace, and 
the bell is closed again. In the “ blast furnace ” ore, or iron oxide, 
is changed to pig iron, which is a combination of iron, silicon, 
manganese, carbon, phosphorus, and sulphur in varying proportions. 

The ore always carries some earthy impurities which are very 
infusible. These are rendered fusible by combination with lime 
used as a “ flux,” and are drawn off as slag. 

The changes which take place in the furnace are as follows: ore 
(Fe 2 0 3 or Fe 3 0 4 +earthy impurities, etc.), fuel (carbon+earthy 
impurities, etc.), flux (limestone, CaC0 3 -bearthy impurities, etc.), 
are introduced into the top of the stack. 

As these move slowly downward their temperature is con¬ 
stantly increased. The ore is first roasted, i.e ., if any car¬ 
bonate be present it is changed to oxide by the driving off of C0 2 ; 
moisture is evaporated; sulphur and arsenic, if present, are oxidized 
and driven off as gases. The limestone is changed from CaC0 3 to 
to CaO by the driving off of C0 2 . The fuel has its temperature 
raised, and if it meets any free oxygen forms CO, and when it 
meets C0 2 also forms CO. 

The lime comes in contact with the silica and alumina, and a 
double silicate of alumina and lime is formed, which going further 
down is melted. 



















































































































































































































































































































































































































































































































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METALLURGY OE IRON AND STEEL. 


13 


The iron oxide, relieved of its silica, alumina, etc., comes in con¬ 
tact with CO and gives up its oxygen for the formation of C0 2 , the 
iron being left in a spongy condition. As this sponge passes further 
down it reaches a zone of higher temperature, and it is probable 
that here in contact with incandescent fuel it absorbs carbon di¬ 
rectly and is carburized; also it is probable that the dissociation 
temperature of CO and C0 2 is reached, and the carbon liberated 
by dissociation is deposited as fine particles in the iron sponge. 
Because of this addition of carbon to the iron, its fusing point is 
lowered, it becomes fluid and runs down with the molten slag into 
the crucible 1), (Fig. 4). Here by reason of its less specific gravity, 
the slag floats upon the iron. Periodically the slag is drawn off 
through a tapping hole between the tuyeres and the bottom of the 
crucible, and then the iron is drawn off through a tapping hole on 
a level w T ith the crucible bottom, and runs into the “ pig bed,” 
where it cools as “ pig iron.” 

The blast of air is forced into the stack near the bottom, and 
immediately meeting incandescent fuel it is changed to C0 2 , and 
immediately afterward to CO. This CO passes on up and is the 
chief agent in the reduction of the iron oxide. In its passage upw r ard 
it alternately meets iron oxide and carbon and is changed to C0 2 and 
then again to CO, and this alternating action continues till a part 
of the stack is reached w T here the temperature is too low for the 
changes to occur. 

It will be seen that the gases issuing from the stack at the top 
will consist of C0 2 , CO, and N. If the fuel is bituminous, 
hydrogen and hydro-carbons will be distilled off near the top of the 
stack, and these wull be found in the issuing gases. The propor¬ 
tions of these constituents vary with the conditions of working of 
the furnace, but there is usually present about 25 per cent. CO, and 
the gas is therefore a gas fuel, and is utilized under the boilers, or 
in the “ hot blast stoves.” 

It has been seen that the flux in the “ direct process ” is iron 
oxide, and that fusible ferrous silicate is formed. This not only 
involves a loss of iron, but also the presence of iron oxide in the 




































































































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METALLURGY OE IRON AND STEEL. 


14 


slag which passes down the blast furnace stack with the iron 
carbide, and is in contact with it in the crucible, would result in 
the decarburization of the iron carbide, or pig iron, which would 
therefore become infusible at the blast furnace temperature and the 
iron could not be drawn off. 

Borne other flux must therefore be used! Lime forms a slag 
with silica and alumina to the exclusion of iron oxide, and for this 
reason is used as a flux in the blast furnace. 

10.—Hot Blast. In the early blast furnaces (and in some of the 
special types still) the blast entered the furnace at the temperature 
of the outside air ; but it was conceived that a gain might result if 
the blast were pre-heated, and this proved true. At first the air, 
on its way from the blowing engine to the furnace, was passed 
through cast iron pipes which were enclosed in a furnace, and 
maintained at the highest* safe temperature for the material of the 
pipes. This temperature, however, is only about 800° jto 900° F., and 
it was desirable to use a hotter blast, and this led to the intro¬ 
duction of hot blast stoves made of more refractory material. 

The Oowper Hot Blast Stove is shown in Fig. 5, with details omitted. 
It consists of an external shell of wrought iron plates, lined with fire 
bricks. C is a combustion chamber, into which the gaseous fuel 
from the top of the furnace is admitted at D, air being admitted at 
B to support combustion. The heated products of combustion pass 
up, over, and down through a chamber A filled with “ chequer 
work,” and out at E to the chimney. During the passage through 
A the heat of the gases is given up to the chequer work, which is 
raised to a white heat after the process has been continued long 
enough. Then, by means of valves, the connections are changed 
so that the air from the blowing engine enters at E and traverses 
the chequer work chamber in a reverse direction, passes down 
through C, and on to the tuyeres, which deliver it into the furnace. 
On its passage through A it is heated to about 1500° F. When the 
stove becomes somewhat cooled the connections are again changed, 
and so the process goes on alternately. 

The Whitwell Hot Blast Stove differs from the Cowper in having 








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METALLURGY OF IRON AND STEEL. 


15 


partitions substituted for chequer work, the gases traversing the 
length of the stove several times. The advantages of the use of hot 
blast may be explained as follows: 

When cold blast is used the temperature of the air entering the 
furnace has to be raised to the temperature of the inside of the fur¬ 
nace, and for this purpose fuel must be burned. If, however, the 
blast is pre-heated, less heating is done inside the furnace, and there¬ 
fore it is not necessary to charge on so much fuel, and a larger 
amount of ore and flux may be charged on in a given time, and 
the output of the furnace is increased. Hot blast therefore results 
in increased economy and increased capacity. Another result of 
the use of hot blast is that a higher temperature is attained in the 
furnace ; and at this higher temperature more carbon and silicon 
are taken up by the iron, and this results in the production of a 
grayer pig iron, such as is used for foundry purposes. Charcoal 
cold blast furnaces produce white pig iron. 

11. —Pig Iron usually contains silicon, manganese, carbon, 
phosphorus, and sulphur. 

The silicon and manganese are reduced from the silica and oxide 
of manganese occuring in the ores. The carbon comes from the fuel 
used; the phosphorus and sulphur may be partly derived from the 
ore and partly from the fuel and flux. Practically the whole 
amount of phosphorus and sulphur appears in the pig iron. 

Pig Iron is either (a) remelted in the foundry cupola, and cast 
into moulds, and so given any required form ; or (b) it is converted 
into wrought iron by the puddling process ; or (c) it is converted 
into steel or ingot iron by the Bessemer process, or by the open 
hearth process. 

12. —Puddling Process. Wrought iron is commercially pure iron; 
i. e., it is iron as nearly pure as can be obtained on a large scale 
economically. It contains from 0.5 to 3 per cent, (according to grade) 
of substances other than iron. 

Pig iron is iron with from 3 to 10 per cent, of other substances, 
either chemically combined or mechanically mixed. 

The object of the puddling process is to change pig iron into 






























































































































































































































































































' 


























































































METALLURGY OF IRON AND STEEL. 


16 


wrought iron. To do this it is necessary to reduce the amount of 
substances other than iron present, and this is accomplished by 
the agency of oxygen. 

There are two puddling processes: 

1st. Dry Puddling. 

2d. Wet Puddling or pig boiling. 

In the first, and less used process the pig iron is melted down 
on the hearth of a reverberatory furnace and an oxidizing flame, 
passing over the hearth to the chimney, gives up its oxygen to 
combine with the silicon, manganese, and iron, to form silica; oxide 
of manganese, and oxide of iron, which combine to form silicate of 
manganese, and also, if there be not an excess of manganese, 
silicate of iron. These silicates are fused and drawn off as 
slag. When the silicon and manganese are completely oxi¬ 
dized, the oxygen attacks the carbon and iron at the surface of 
the molten metal. The CO and C0 2 formed pass off to the stack, 
and the FeO acts as a carrier of oxygen; i.e., it is mixed with the 
bath and gives up its oxygen to combine with the carbon of the 
iron carbide, and the result is that CO bubbles up to the surface of 
the bath and burns there to C0 2 , while the iron of the oxide and 
carbide remain in the hearth. This continues till the carbon is 
almost entirely removed. Then, because of the reduction of the 
fusing point, the iron begins to solidify and is collected in a 
“ puddle ball,” which is really a sponge of wrought iron with its 
interstices filled with slag, and is raised to a welding temperature, 
and put through a “squeezer” where the slag is squeezed out 
and the component parts are welded together. It is thereby con¬ 
verted into a “ bloom.” This bloom is then put through a “ rough¬ 
ing train ” of rolls and is thereby converted into “ muck bar,” which 
is cut up, piled, reheated, and rolled into “ merchant bar.” This 
piling, heating, and rolling is sometimes repeated, with a resulting 
product of finer fibre, and increased strength and ductility. 

The second, and more commonly used process, differs from the 
first only in the fact that the iron oxide, which is the carrier of 
oxygen, instead of being obtained by oxidizing the surface of the 







































































METALLURGY OF IRON AND STEEL. 


17 


bath with an oxidizing flame, is charged into the hearth in the 
form of “ mill scale,” cinder rich in FeO, or some kind of rich ore, 
as haematite or magnetite. 

In the puddling process a part of the sulphur is eliminated. 
The phosphorus may be much reduced in amount, appearing in the 
slag as phosphoric acid. The amount of phosphorus removed 
seems to vary inversely with the temperature. Gray iron is not 
suitable for the puddling process because (a) it contains too large 
an amount of silicon, which has to be removed with the production 
of a large amount of slag, and (b) because when melted it becomes 
quickly fluid on reaching its melting point, whereas white iron 
passes through an intermediate pasty state which is favorable to 
the puddling process. It may be economical, however, to run the 
blast furnace on gray iron, even if its product is to go to the pud¬ 
dling furnace. 

13. —This leads sometimes to the use of an intermediate process, 
called refining. The iron, either direct from the blast furnace or as 
pig iron, is run or charged into the rectangular hearth of a furnace 
called a “ refinery,” and subjected to a strong air blast. The silicon 
and manganese, and perhaps a little of the carbon, are oxidized out 
(in some cases only silicon), and the gray pig iron is thereby con¬ 
verted into white iron. 

14. —Processes for making tool steel from wrought iron. 

The difference between wrought iron and tool steel is in the 
amount of carbon cor L ,ained. 

Wrought iron has from 0.1 to 0.3 per cent. 

Tool steel “ 0.5 to 1.25 “ 

The change from wrought iron to tool steel is therefore to be 
effected by addition of carbon. 

Cementation Process.—Bars of very pure wrought iron, about 
f"x5"xl2 feet long are packed in refractory boxes about 3 feet 
wide by 3 feet deep, with alternate layers of rather finely di¬ 
vided charcoal. These boxes, which are sealed up to exclude the 
air, are in a furnace where the temperature is gradually raised to 
3 




METALLURGY OF IRON AND STEEL. 


18 


about 3000° F. and maintained for several days, and then allowed 
to cool down. Iron in contact with carbon at high temperature 
tends to absorb carbon slowly, and it is found that the bars, after 
treatment as described, are changed to steel. The carbon, however, 
is not uniformly distributed, and the structure is coarse, and the 
material brittle. This material (called blister steel) is changed to 
tool steel by the crucible process. 

The blister steel is broken up into small pieces and charged 
into refractory crucibles about 2 feet high, with an average diam¬ 
eter of about 10". These crucibles are placed in a furnace where 
the melting temperature of steel can be attained, and are left till 
their contents is fused. This is then cast into an ingot, which is 
homogeneous chemically, but, of coarse, crystalline structure, be¬ 
cause of its heat treatment. It is then reheated and hammered into 
standard sizes and forms, and the mechanical working gives it a 
fine homogeneous structure. 

15.—The Bessemer Process. Bessemer steel is very similar to 
wrought iron in chemical composition, but usually contains a 
slightly larger amount of carbon. The structure however, is dif¬ 
ferent because of the different method of manufacture. The 
Bessemer process changes pig iron to steel, or ingot iron, con¬ 
taining from 0.1 to 0.6 per cent, carbon. This change is ac¬ 
complished in a vessel called a converter, the general form being 
as shown in Fig. 6. The vessel is made up of iron plates 
riveted together and lined with “ ganister,” a refractory ma¬ 
terial composed chiefly of silica. It is mounted upon trunions 
whose axis is at A, and it may be rotated about this axis into 
any position, by hydraulic power. In the removable bottom is 
a chamber, B, into which cold air is forced under a pressure of 
about 25 lbs per square/ inch. Holes about f" diameter connect 
this chamber with the inside of the converter. 

The converter is turned into the position shown in Fig. 7, and 
melted pig iron is run in as shown. It will be seen that the sur¬ 
face of the metal must not reach the “ tuyeres holes.” The con¬ 
verter is now turned into a vertical position, and an automatic, 








* 

















































































































METALLURGY OF IRON AND STEEL. 


19 


valve is provided so that the blast is turned on as the converter is 
turned up, and the tuyeres holes are thus kept clear. 

Air is now forced continuously through the metal bath. The 
results are as follows : The oxygen of the air combines with the 
oxidizable substances of the bath; and iron being in great excess FeO 
is formed throughout the entire “ blow.” But silicon is also pres¬ 
ent, and the FeO is reduced by it, and silica is formed thus, as well 
as by direct combination of silicon with the oxygen of the air. 
Manganese is also present and oxide of manganese is formed, and 
this combines with silica to form silicate of manganese, a fusible 
slag. If the silica is in excess some fusible silicate of iron is also 
formed. During this period brilliant sparks (slag) are thrown 
from the mouth of the converter. 

When all the silicon and manganese are removed, the carbon 
begins to be oxidized, directly by the oxygen of the air, and in¬ 
directly by the oxygen of the FeO. CO is formed, which passes off 
from the bath, and on reaching the mouth of the converter burns 
to C0 2 in a long, bluish flame. When the reduction of the carbon 
is complete, there is no substance left to reduce the iron oxide formed, 
and reddish fumes appear at the mouth of the converter. The 
process is then immediately stopped by turning the converter on its 
side. 

The converter now contains nearly pure iron, and although its 
fusion temperature is about 4000° F., it remains fluid. The fuel 
which, by its oxidation or combustion, has raised the temperature 
of the converter from the melting point of pig iron to that of 
wrought iron, is the silicon, manganese, and carbon of the pig iron. 

When the first experiments were made on the Bessemer pro¬ 
cess, it was thought that the process could be stopped at the right 
point to leave in the amount of carbon necessary to make steel; but 
it was found impossible to get uniform results, and also it was 
found that the resulting metal was brittle and worthless. This 
was due to the fact that iron oxide remained in the metal, and 
that some gas was occluded, causing porosity. To overcome these 
difficulties, the blow was continued till the carbon was completely 




METALLURGY OF IRON AND STEEL. 


20 


removed, and a known proportion of “ spiegel eisen,” or ferro-man- 
ganese (compounds of iron, manganese, and carbon) was added to 
effect the recarburization. The manganese was found to reduce the 
iron oxide, and, in some not very well understood way, to remove 
the occluded gases. After the addition of the “ spiegel ” or “ ferro,” 
the contents of the converter is poured out into a ladle, from which 
it is cast into ingots, which are rolled into rails, or plates, or into 
blooms, which are to be rolled into the standard forms for the 
market. 

16.—The Basic Bessemer Process. Phosphorus may be removed 
from cast iron as follows : Phosphoric acid, P 2 0 6 , and FeO are 
formed simultaneously, and these combine to form phosphate of 
iron, or ferrous phosphate; thus 3Fe0+P 2 0 5 —Fe 3 P,0 8 . But this is 
reduced again to iron phosphide by silicon and carbon, and therefore 
little or no phosphorus can be removed until after the complete 
removal of these substances from the metal in the converter. Ferrous 
phosphate is also reduced by silica, because the silica has greater 
affinity for FeO than phosphoric acid has, and so ferrous silicate 
is formed and phosphoric acid is left, which is probably reduced 
to iron phosphide by the metallic iron, with formation of FeO. 

The lining of the Bessemer converter described is largely silica, 
and therefore silica is always present, and no phosphorus can be 
removed in a converter with a “ ganister ” or “ acid ” lining. It 
is necessary, therefore, to use pig iron for this process which is 
very low in phosphorus, since the presence of phosphorus in the 
product in any considerable amount is very undesirable. 

The fact that a large proportion of the iron ore of the world 
contains phosphorus, which is not removed in the blast furnace, 
made it desirable to find a way to eliminate phosphorus in the steel 
making process. This led to the invention of the Basic Bessemer 
Process, in which a lining of lime and magnesia is substituted in 
the converter for ganister. The only free silica then is that which 
results from the oxidation of the silicon in the pig iron. This com¬ 
bines with the lime or magnesia of the converter lining, or with 
that which is charged into the converter during the blow, and forms 






















METALLURGY OF IRON AND STEEL. 


21 


a stable slag, the silica being thereby rendered powerless to reduce 
the ferrous phosphate. 

The lime or magnesia present then replaces the FeO of the fer¬ 
rous phosphate, forming calcium or magnesium phosphate, which is 
probably the form in which the phosphoric acid chiefly exists in 
the slag. 

In the acid process iron is not used which contains less than 2 
per cent, of silicon, because the combustion of at least that amount 
of silicon is necessary to produce a sufficiently high temperature in 
the converter. 

In the basic process it will be seen that silicon is an undesirable 
element, since all the silica produced must be neutralized by lime, 
in order that the process shall succeed. For this reason iron with 
0.5 per cent, silicon is best, and 1.5 per cent, is the highest allow¬ 
able limit. This makes it necessary to substitute some other fuel, 
and therefore pig iron high in manganese is used. The phosphorus 
is also a fuel and raises the temperature during the “ afterblow.” 
In the basic process little or no phosphorus is removed till after the 
complete removal of the carbon, and the blow has to be continued 
after the “ dropping ” of the carbon flame. The duration of the 
afterblow is determined from a knowledge of the phosphorus con¬ 
tent of the pig iron used, or by taking samples at intervals during 
the afterblow and making physical tests. 

The best pig iron for the basic process contains: 

P, about 3. per cent. 

Mn, over 2. “ 

Si, 0.5 “ 

S, less than 0.1 “ 

This is white iron, because of high manganese and low silicon, 
whereas the high silicon iron used in the acid process is gray. 

17.—Control of temperature in the Bessemer Converter. Either too high 
or too low temperature of the steel at pouring results in porosity, 
and therefore this temperature must be carefully regulated. If iron 
too high in silicon be used in the acid process, too high temperature 
results, and conversely. 



METALLURGY OF IRON AND STEEL. 


22 


In the basic process the difficulty is usually to keep the temper¬ 
ature high enough. If the temperature is too high it may be re¬ 
duced by charging in scrap steel from the mill, which is thus re¬ 
melted, absorbing surplus heat, and is rendered available for use. 
The temperature is also sometimes reduced by admitting a small 
amount of steam into the blast pipe. 

If the temperature becomes too low the converter may be in¬ 
clined, as shown in Fig. 8, during the burning out of the carbon. 
When the converter is vertical the CO formed burns at the mouth 
of the converter, and the heat evolved is lost as far as raising the 
temperature of the inside of the converter is concerned. In the in¬ 
clined position, however, part of the air of the blast passes through 
the metal bath and forms CO, and part passes through the uncov¬ 
ered tuyere holes and furnishes oxygen to # the CO, and C0 2 is 
formed ; i.e combustion occurs inside of the converter, and the 
heat developed raises the temperature of the metal bath. 

18.—Open Hearth Processes. Steel is also made from pig iron in 
the hearth of a Siemens regenerative furnace. The silicon, man¬ 
ganese, and carbon are removed by oxidation, as in the puddling, 
or Bessemer process. Two processes are carried on in open hearth 
furnaces: 1st, Siemens, or “pig and ore” process; 2d, Siemens- 
Martin, or “ pig and scrap ” process. These correspond to wet and 
dry puddling; the difference being that here the temperature is 
high enough so that the product is held fluid and cast into an ingot, 
while in the puddling process the temperature is such that the 
product solidifies and must be treated by rolling mill processes. In 
the Siemens process, pig iron is charged into the hearth and melted, 
part of the silicon and manganese being oxidized during the 
melting, and then rich ore is added to supply the oxygen to com¬ 
bine with the remaining silicon and manganese, and the carbon of 
the iron carbide. When the action is complete the bath of nearly 
pure iron is recarburized by the addition of “ spiegel eisen ” or 
ferro-manganese, and the manganese reduces the FeO present and 
removes occluded gases as in the Bessemer process. 

In the Siemens-Martin process pig iron is charged into the hearth, 


























































































































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METALLURGY OF IRON AND STEEL. 


23 


and melted with partial removal of the silicon and manganese, and 
then steel scrap is charged into the bath, which melts, and thus the 
percentage of silicon, manganese, and carbon is reduced by dilution. 
The remaining part of these substances is removed by the direct 
action of the oxidizing flame, and the indirect action of the FeO 
formed at the surface of the bath, and mixed with it. “ Spiegel ” or 
“ ferro ” are added as in the Siemens process. Ferro-silico’n and 
ferro-aluminum are sometimes used in place of ferro-manganese for. 
the recarburization, and the removal of iron oxide and the prevent¬ 
ion of porosity. 

19.—Ductile Castings. Many machine members of somewhat com¬ 
plicated form need to be of material whose ductility and resilience 
are high. If such parts were to be made in large numbers, they 
could be produced by the process of casting much cheaper than by 
the process of forging. For this reason much attention has been 
given to the production of castings of ductile material. The most 
important resulting processes are those for the production of : 1st, 
Malleable Castings ; 2d, Steel Castings. Some of the grades of brass 
and bronze give castings which are strong and ductile, but the high 
cost puts them out of competition for many purposes. These will 
be considered later. 

1st. The process for the production of Malleable Castings. AVhite 
cast iron, i.e., iron with all the carbon in combination, is melted 
in a cupola and cast into the required forms. These castings, 
which are hard, weak, and brittle, are packed in cast iron 
boxes in the midst of coarsely powdered oxide of iron -usually 
haematite ore or hammer scale. These boxes are sealed and exposed 
to a temperature of full redness in a reverberatory oven, for from 
three to six days. They are then slowly cooled down, and it is 
found that the amount of carbon near the surface of the castings is 
so much reduced that the cast iron is changed to something that is 
very like wrought iron in strength, ductility, resilience, and softness. 
This is, however, only a surface process, the “mallifying” not ex¬ 
tending very far inward from the surface. The process is, therefore, 
only applicable to castings of small cross sections. To make it also 



METALLURGY OF IRON AND STEEL. 


24 


applicable to larger castings, the iron is melted in the hearth of a 
reverberatory furnace called an “air furnace,” and the silicon (if 
any he present), manganese, and carbon are oxidized by the direct 
action of an oxidizing flame, and the secondary action of the iron 
oxide which is formed, until the iron contains the least amount of 
carbon that it can contain and still be satisfactorily cast. It is, 
therefore, a step nearer wrought iron than the castings from the 
cupola, and the effect of “ mallifying ” extends deeper, and the 
inner parts which are little affected are stronger, more ductile, and 
more resilient than the inner parts of cupola melted castings. This 
same result is sometimes accomplished by adding wrought iron 
scrap to the white iron in the cupola. This reduces the amount of 
carbon by dilution. These castings are mallifled, and are often in¬ 
correctly called “ steel castings.” 

2d. Steel Castings. The high temperature which is attainable by 
means of the Siemens regenerative furnace, makes it possible to 
melt “open hearth ” or “ Bessemer” steel so that it is fluid enough 
to “ run sharp ” in castings, and these castings are steel castings. 
Since the “freezing point” of these grades of steel is about 1000° F 
higher than that of cast iron, it follows that all the ill effects of 
“shrinkage” in cast iron are intensified in steel castings. Because 
of this nearly all steel castings require to be annealed to remove the 
internal stresses resulting from shrinkage. Spongy metal and 
“ blowholes ” are often a hidden source of weakness in steel castings. 

20.—Nomenclature of iron and steel. Since the introduction of the 
Bessemer and open-hearth process, there has been great lack of ex¬ 
actness in the use of the term “ steel.” A product of the Bessemer 
procees, for instance, may have almost identical composition with 
a product of the puddling process, the only difference between the 
two being a difference of structure, which is due to the method of 
manufacture (the iron being built up by welding, while the steel 
is rolled from a single piece); yet one is called steel, while the other 
is called iron. The Bessemer metal (usually) has not enough car¬ 
bon to “ harden,” and therefore, has not that claim to the name 
“ steel.” 





METALLURGY OF ‘IRON AND STEEL. 


25 


An international committee appointed in 1876 recommended a 
nomenclature which in brief is as follows : 

Malleable compounds of iron, and the other substances usually 
mixed with it, when they are formed by welding, and will not 
sensibly harden, are called weld iron. 

Compounds of iron as above, when they are formed by welding, 
and will sensibly harden, are called weld steel. 

Compounds of iron as above, when they are formed by casting 
into ingots from a fluid state, and will not sensibly harden, are 
called ingot iron. 

Compounds of iron as above, when they are formed by casting 
into ingots from a fluid state, and will sensibly harden, are called 
ingot steel. 

This seems an excellent nomenclature. But a new system 
which is designed to replace another already in use is slow of 
adoption. And in this case, that which really should be called 
ingot iron, is called steel, and probably will be for a long time. 

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CHAPTER II. 


Representation and Interpretation of the Physical Qualities 

of Materials. 

20.—The testing of materials', and the methods of recording and 
interpreting results, will he briefly considered, as a preliminary to 
the work which follows. 

A test piece of proper dimensions may be made of any material, 
and may be broken by the application of a force producing tensile, 
compressive, torsional, or transverse stress. It will be assumed 
that means are provided for the application of forces of known 
value ; also that any deformation of the test piece may be accur¬ 
ately measured. Let a tension test be considered. The force in 
this case is applied so that it tends to elongate the test piece. The 
elongation which results is called “ strain.” The action and re¬ 
action between adjacent portions of material is “ stress.” Strain is 
always the deformation which accompanies stress. 

It will be found that for every increment of stress there will be 
an increment of strain. In the early part of the test these will be 
proportional to each other ; i.e ., stress is proportional to strain. This is 
“ Hooke’s Law.” After passing a certain limit it is found that this 
proportionality ceases; the increment of strain becoming much 
greater for a given increment of stress. This limit is called the 
elastic limit of the material. 

If, before reaching this limit the stress be gradually reduced to 
zero, the strain will become zero ; i.e., the test piece will return to 
its original dimensions showing that the material is perfectly 
elastic; since elasticity is the quality of returning to original dimensions 
































































* 


























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- - 














































V 




























































REPRESENTATION OF PHYSICAL QUALITIES. 


on the relief of stress. If, however, the elastic limit be passed before the 
relief of stress, the test piece will be found to be permanently elon¬ 
gated. This permanent elongation is called “set” or permanent strain. 
The strain within the elastic limit is called elastic strain. 

If the test be continued, it will be found that the ratio of stress 
to strain continually decreases after passing the elastic limit. 
After a while a point is reached where no further increase of stress 
can be made, because every effort to increase stress is met by so 
great yielding. The stress at this point is called maximum stress, 
and it represents the breaking or ultimate strength of the material. 
From this point on there is an increasing strain and a decreasing 
stress, till the test piece is ruptured. 

Up to the time of reaching the maximum stress, all elementary 
units of length of the test piece share the elongation equally. If 
the piece were of absolutely equal strength in all sections, it would 
continue to elongate equally throughout and would finally yield in 
all sections at once. This is, of course, impossible, and the point 
of maximum stress is really the point at which some local weak¬ 
ness is developed, and there then occurs a localization of strain, i.e ., 
the test piece “ necks down,” and from that point on till rupture 
the elongation occurs in the neck, because the unit stress (stress 
per square inch of section) becomes greater with the local reduction 
of cross sectional area. This does not occur in brittle materials, 
but stress increases from the beginning of the test till rupture 
occurs. 

The test may be made continuous from the beginning without 
relief of stress, and if periodical readings of stress and correspond¬ 
ing strain be taken, these variables may be plotted with reference 
to rectangular axes, and a curve drawn through the points so 
located will be the stress-strain diagram of the material. The test 
described is that of a ductile material, and B, Fig. 10, represents 
the stress-strain diagram which would be obtained. A brittle ma¬ 
terial gives a diagram entirely different in character. Thus C, 
Fig. 10, may represent a stress-strain diagram of cast iron. If dia¬ 
grams of different material be plotted on the same scale, their 






























































































REPRESENTATION OF PHYSICAL QUALITIES. 


28 


physical qualities may be compared by inspection of the dia¬ 
grams. 

21.—The physical qualities which appear on the stress-strain 
diagram are as follows : 

1st. Strength at elastic limit. 

2d. Strength, ultimate. 

3d. Ductility. 

4th. Stiffness. 

5th. Elasticity. 

6th. Resilience, elastic. 

7th. Resilience, ultimate. 

Strength at elastic limit is measured by the stress per unit of cross 
sectional area of the piece when the proportionality of stress and 
strain ceases. Ultimate strength is measured by the stress per unit of 
cross sectional area when the yielding becomes so great that no 
addition can be made to the stress. Ductility is the quality of being 
drawn out under stress, and is therefore proportional to the strain, 
and to the length of the stress-strain diagram on the axis of X. 
Stiffness is the quality of resisting yielding, or strain within the 
elastic limit. It is therefore measured by the angle which the 
Hooke’s law line makes with the axis of X. The greater this 
angle the greater the stiffness of the material. Elasticity is already 
defined as the quality because of which a material regains its orig¬ 
inal dimensions on the relief of stress. Resilience is work done. 
Elastic resilience is the work done in straining a piece of material to 
its elastic limit. Ultimate resilience is the work done in breaking a 
piece. Since resilience is the work done in producing strain in 
material, it is therefore a measure of the shock resisting power of 
the material, i.e., it represents the energy of a shock or blow which 
would produce the same result. Since the ordinates of the stress- 
strain diagram represent force, and the abscissas represent the 
space through which the force acts, it follows that the area of the 
diagram represents work. If, then, a perpendicular be dropped 
from the elastic limit of the diagram to the axis of X, a triangle 
will be formed whose area is proportional to the elastic resilience 




























































































REPRESENTATION OF PHYSICAL QUALITIES. 


29 


of the material. Thus in Fig. 10 the triangle OEH is a measure of 
the elastic resilience of the material represented by the curve B, 
and the triangle OE'K is a measure of the elastic resilience of 
the material represented by the curve A. If a perpendicular be 
dropped to the X axis from the end of the diagram, it will be seen 
that the area bounded by this perpendicular, the curve of the dia¬ 
gram, and the axis of X, will be a measure of the ultimate resil¬ 
ience of the material. Let a comparison of all of these qualities be 
made for the materials represented by the diagrams of Fig. 10. The 
curve C rises with a continuous curvature ; there is no straight part 
denoting a period of proportionality of stress and strain ; or, in 
other words, there is no elastic range. There is also no limit of 
elasticity. If stress were discontinued at F, the curve would not 
return upon itself, but would follow an approximate straight line 
to G, some point to the right of O. This indicates that there is a 
permanent strain or “ set ” whose value is OG on the scale assumed 
for plotting strains. A similar effect would be shown if the stress 
were relieved at any point in the curve. The material represented 
by this curve is therefore imperfectly elastic. The same is true of 
the curve I), which may represent a grade of brass. The straight 
Hooke’s law line of the curves A and B, however, indicate perfect 
elasticity.* 

The elastic strength of the material of A, Fig. 10, is greater than 
that of B in the ratio of the ordinate E'K to EH. C and D have no 
elastic limit and, therefore, no value of elastic strength can be 
assigned. The ultimate strength of A is measured by the ordinate 
MN ; of B by M'P ; of C by M"L; and of D by M"'R, and so the 
comparison is easily made. 

The ductility of A is measured by OS'; of B by OT'; of C by OL; 
and of D by OV'. 

* It probably is not absolutely true that this material is perfectly elastic. By 
means of very refined measuring apparatus it is found that nearly all materials 
take some “set,” even when subjected to comparatively small stress. The 
values, however, are so minute that they may be safely disregarded in the selection 
of materials for machine parts. 










REPRESENTATION OF PHYSICAL QUALITIES. 


30 


The elastic resilience of A is measured by the area OE'K ; of B by 
OEH. No elastic resilience can be assigned to C and D since they 
have no elastic limit. 

The ultimate resilience of A is measured by the area OE'MSS'; of 
B by the area OEM'TT'; of C by the area OFM'L ; and of D by the 
area ODM'"VV'. Stiffness, being proportional to the angle of the 
initial part of the curve with the axis of X, is in the following order, 
beginning with the stiffest material : 1st, A , 2d, B ; 3d, C ; 4th, D. 

If a material be tested in compression as well as in tension, both 
stress and strain will be reversed, and stresses will be plotted below 
the axis of X, and strains will be plotted toward the left from the 
axis of Y. Fig. 11 shows stress-strain diagrams of cast iron and 
Bessemer steel, both in tension and compression. The compression 
curve of the steel is almost identical with the tension curve, up to 
and past the elastic limit. A ductile material cannot, however, be 
tested to rupture in compression as the material either “ buckles,” 
splits parallel to the axis of the test piece, or else simply flattens 
out, thus exposing a constantly increasing area of section to the 
crushing force. A brittle material breaks in compression by shear¬ 
ing off on planes at an angle of about 45° with the axis of the test 
piece. The diagram shows that cast iron is a much stronger mater¬ 
ial in compression than in tension. 

Stress-strain diagrams may be also plotted from the data of 
torsion and transverse tests, as well as from those in which the 
stress is tensile or compressive. 







































CHAPTER III. 


Variations of the Physical Qualities of Cast Iron, Their 
Causes, and Control. 


22.—Cast iron, as has been stated, is composed of iron,' carbon, 
silicon, manganese, sulphur, and phosphorus. Wrought iron has 
usually the same qualitative composition, but the substances other 
than iron, are reduced to the very lowest limit possible commercially. 
Thus the “ puddling process,” which converts cast iron into wrought 
iron, accomplishes its object by oxidizing out all that is possible of 
the (in this case) undesirable elements. The percentage range of 
these substances in wrought and cast iron is shown in the following 
table : 


Cast iron 


Graphitic Combined Total 

Carbon. Carbon. Carbon. 

1.85 to 3.25 .15 to 1.25 2. to 4.5 


gauos'e. v loZ. 

.15to5. 0 to 1.5 Oto.5 0tol3 


Wrought iron .02 to .25 Oto.2 0 to .3 Oto.015 Oto.15 


Although the only chemical difference is in the amount of these 
substances present, yet the physical qualities are entirely different, 
as will be evident on inspection of curves A and B, Fig. 10. B may 
represent wrought iron, and C may represent cast iron. In the 
change from wrought to cast iron the material has become weaker, 
less elastic, less stiff, less ductile and less resilient ; but stronger in 
compression (see Fig. 11). It would seem that it had become in all 
respects, except for resisting compression, a less desirable material 
for use in machine parts. There is, however, one quality of which 
there is no record on a stress-strain diagram, and because of which 
cast iron is invaluable for many machine parts. It is the quality 
of fusing at a temperature which is easily attainable in the ordinary 



PHYSICAL QUALITIES OF CAST IRON. 


32 


foundry cupola. Because of this quality it may be cast into sand 
moulds, and so takes any required irregular shape, such as cannot 
be produced by forging; and, after a pattern is once made, a large 
number of duplicates can be easily and cheaply produced. Where 
cast iron machine members are “ stress members,” the deficiency in 
strength is compensated by increased cross sectional areas. Cast 
iron melts at a temperature of about 2500° F, while the temperature 
of fusion of wrought iron is about 4000° F, or the highest tempera¬ 
ture attainable in the Siemens Regenerative Furnace. Wrought 
iron cannot, therefore, be cast (except by special means), and hence, 
has to be shaped by forging. Cast iron cannot be forged at all, and 
does not possesss the quality of welding which is so important in 
the case of wrought iron. 

23. —The carbon in cast iron usually exists in two forms ; a part is 
combined, or in solution with the iron, and a part is in the form of 
crystals of graphite distributed throughout the mass of the iron. 
The reason for this is as follows : When cast iron is in a fluid state 
it has a certain capacity for taking carbon into solution. This 
capacity is very much reduced when the iron begins to solidify. If, 
therefore, the fluid iron has absorbed more carbon than it is capable 
of holding when it is solidifying, the excess will crystalize out as 
graphite ; and, since this crystalization occurs after the iron has 
ceased to be 'wholly fluid, the graphite crystals remain suspended 
in the iron, notwithstanding their less specific gravity. 

24. —The Blast Furnace produces different grades of cast iron, which 
are numbered usually from No. 1 to No. 6. No. 1 is very gray at 
the fracture, and contains a large amount of graphite. No. 6 is 
white at the fracture, and all the carbon is in the combined state. 
The intermediate numbers represent the gradation from one to the 
other. The total carbon in cast iron depends chiefly upon the type 
and conditions of working of the furnace. The distribution of the 
total carbon between combined and graphite is dependent upon the 
relative amounts of the other substances present. The amount of 
total carbon may also be influenced by the presence of the other 
substances. 





PHYSICAL QUALITIES OF CAST IRON. 


33 


25.—Cast iron depends for its physical qualities upon the effect 
of the silicon, manganese, carbon, sulphur and phosphorus, with 
which it is mixed or combined ; and also upon the effect of these 
substances upon each other. 

The effect of graphitic carbon upon cast iron is to make it weak 
both in tension and compression, and to reduce its ductility. This 
effect is probably due to the fact that the presence of the crystals 
of graphite interrupt the continuity of the iron structure. Graph¬ 
itic carbon also renders the iron softer ; probably because of the in¬ 
troduction of a softer material, and also because the introduction 
of graphitic carbon is usually at the expense of the combined car¬ 
bon, which hardens the material. 

The addition of combined carbon in successively increasing 
amounts to wrought iron converts it, first into soft steel, then into 
tool steel, and finally into cast iron. This change is accompanied 
by steadily increasing strength, and steadily decreasing ductility. 

Thus in Fig. 12, if A represent the stress-strain diagram of 
wrought iron, the gradual increase of carbon would gradually 
change it into a material represented by the stress-strain diagram, B.; 
the strength being increased from GF to IIE, while the ductility 
is reduced from 01) to OE. The compressive strength and ductility 
would be similarly changed. Sometime after passing 1.5 per cent. 
C (which is generally recognized as about the dividing point be¬ 
tween tool steel and cast iron), the addition of further amounts 
of carbon decreases the tensile strength, with still further decrease 
of ductility, and increases the compressive strength. Thus in Fig. 
13, the stress-strain diagram, B representing tool steel, 1.5 per cent, 
carbon, is, by gradual increase of carbon, converted gradually into 
the stress-strain diagram C, representing cast iron. It follows then 
that the effect of combined carbon on cast iron is to decrease ten¬ 
sile strength and ductility, and to increase compressive strength 
and hardness. The effect of combined carbon is greater in degree 
than that of graphitic carbon, i.e., one per cent, of combined carbon 
makes changes that are greater in amount than would be made by 
one per~cent. of graphitic carbon. If an iron be selected having a 
5 ~ 



'-D\ 











































PHYSICAL QUALITIES OF CAST IRON. 


34 


certain total carbon (say 3.5 per cent., which is about the average 
for foundry use), and if all this carbon he in the form of combined 
carbon, i.e ., no graphitic carbon present, the selected iron will he a 
brittle, hard material, weak in tension, and strong in compression, 
and might he represented by the curve C of Fig. 13. If now a 
part of the combined carbon be converted into graphitic carbon, the 
result will be as follows : The tensifyle strength and ductility will 
be increased, because the reduction of combined carbon has in¬ 
creased both of these qualities, and the increase of graphitic carbon 
has reduced both of these qualities, but the reduction is less than 
the increase, because the effect of the graphitic carbon is less in 
degree than that of the combined carbon, and the resultant effect is 
an increase of tensi^le strength and ductility. The compressive 
strength is decreased because both the decrease of combined carbon, 
and the increase of graphitic carbon tend to produce that result. 
The material is rendered softer both by the reduction of combined 
carbon and the increase of graphitic carbon. Since this change 
has increased both tensile strength and ductility, it follows that the 
tensile resilience, and hence the tensile shock resisting power of 
the material is increased, while the compressive shock resisting 
power is decreased. The reversal of this process would, of course, 
produce reverse results. If, now, the control of the distribution of 
total carbon between graphitic carbon and combined carbon were 
possible, it would become possible to control, at least in part, the 
qualities of castings so as to fit them for different purposes. 

26.—The rate of cooling of castings has a very marked effect upon 
the crystalizing out of the graphitic carbon. Thus, if a certain iron 
with a low total carbon (most of which is held in combination), be 
melted and cast into a mould, a part of whose internal surface is of 
sand, and another part of iron, the part of the molten metal which 
comes in contact with the iron surface will be cooled far more rap¬ 
idly that the part that comes in contact with the sand surface (be¬ 
cause of the greater conductivity of the iron). The result will be 
that the part of the casting which has been “ chilled ” will be white 
in fracture, showing that the carbon is all in combination ; while the 









* 




\ 



















































* 


\ 








% 
































PHYSICAL QUALITIES OF CAST IRON. 35 

other parts of the casting will be somewhat gray, showing that a 
part of the carbon has crystalized out as graphitic carbon. The 
reason for this effect is that the crystals of graphite need some time 
to form, and the sudden cooling does not allow this time, and the 
carbon remains all as combined carbon. This is taken advantage 
of when it is required to produce a casting which must have hard 
surfaces in certain parts to resist wear, while other parts must be 
soft enough so that they may be worked in the shop, and must also 
have sufficient resilience so that continuously repeated shocks shall 
be safely resisted, as in the case of car wheels, or “ chilled ” rolls 
for iron mills. 

27.—The most effective method for controlling the distribution 
of carbon is that of regulating the amounts of the other substances 
present, viz : Silicon, manganese, sulphur, and phosphorus. 

If gray iron be melted, and a considerable quantity of manganese 
be added (in the form of ferro-manganese), the iron will be found on 
cooling to have a white fracture, showing that the carbon which 
before was graphitic carbon is now taken into combination. If, on 
the other hand, white iron be melted, and a considerable quantity 
of silicon be added (in the form of ferro-silicon), it will have a gray 
fracture on cooling. This shows that some of the combined carbon 
has been converted into graphitic carbon. The tendency of the 
presence of manganese is, therefore, to increase the capacity of iron 
for holding carbon in combination, while the presence of silicon has 
the reverse tendency. 

The presence of sulphur or phosphorus has also a decided effect 
upon the distribution of carbon, tending in both cases to increase 
the amount of combined carbon. If these elements are introduced 
in any considerable quantity, they render the iron unsafe for stress 
members of machines, and especially if they are subjected to shock. 
Sulphur should not exceed 0.15 per cent., and phosphorus should 
not exceed 0.3 per cent. These elements, therefore, should not 
be used for regulating the carbon distribution. The ill effects, 
however, which result from the use of silicon or manganese for this 
purpose are comparatively small. Mr. T. Turner, of Mason College, 










' 





















. 














































































































































t 








. ' 
















































































































































■1 





























































































































PHYSICAL QUALITIES OF CAST IRON. 


36 


Birmingham, has done excellent work in the determination of the 
effect of silicon on cast iron. He took iron which had a total carbon 
as nearly as possible 2 per cent., and with sulphur, phosphorus, and 
manganese quite low ; and by means of ferro-silicon, added success¬ 
ively increasing amounts of silicon, and then subjected the products 
to chemical and physical tests. The results of these tests as to 
tensile and compressive strength and hardness are plotted in Fig. 
14. It will be seen that the compressive strength is a maximum 
with the percentage of silicon (measured on the axis of X), between 
0.5 per cent, and 1 per cent. ; that the tensile strength is a max¬ 
imum at 2 per cent, silicon, and that the softest iron is that con¬ 
taining between 2 and 3 per cent, silicon. Since a force applied 
transversely induces both tensile and compressive stress, it follows 
that the maximum resistance to transverse force is when the per¬ 
centage of silicon is between 0.5 per cent, and 2 per cent. No data are 
given to show ductility, and hence no curve of resilience can be 
plotted. It is probable, however, that the curve of tensile resilience 
would follow approximately the curve of tensile strength, and that 
the curve of compressive resilience would follow approximately the 
curve of compressive strength. 

28.—A varied quality of product is required from a foundry. 
Some castings are not subjected to any considerable stress, and the 
main requirement is that they shall be soft and “run sharp;” i.e., 
that they shall take accurately the form of the mould. The crystal- 
izing out of the graphite causes a.reduction of the shrinkage of the 
iron in cooling. This result might reasonably be expected, since the 
formation of graphite, whose specific gravity is much lower than 
that of iron, must reduce the specific gravity of the whole mass ; i.e., 
a given weight of graphitic iron would occupy a larger cubic space 
than if the carbon were all combined. This, in part, counteracts 
the effect of the natural shrinkage of the iron, and so the castings 
fill the mould better. Iron with a large proportion of graphitic 
carbon is most satisfactory for soft sharp castings. This means 
iron with a large proportion of silicon. Fig. 14 shows, however, 
that for maximum softness, silicon should'not exceed 3 per cent. 




PHYSICAL QUALITIES OF CAST IRON. 


37 


Other castings require to be as strong as possible in tension, and 
yet soft enough to be worked economically in the machine shop, 
and also hard enough to resist wear. The maximum tensile 
strength coincides with almost the softest iron at 2 per cent, silicon. 
Jt is better to sacrifice something of tensile strength, to gain in 
hardness and compressive strength, and hence, about 1.5 per cent 
silicon would probably he best for machine castings. If a casting 
were required capable of withstanding severe compressive shocks, 
as for instance an anvil block for a steam hammer, then, since 
very little machine finishing needs to be done upon it, a material 
should he selected with the maximum compressive strength, al¬ 
though the hardness is very much greater. 

If castings are required for “ chilling ” or for the process of 
malleablizing, they must he very low in silicon, as the presence of 
any very considerable amount of the graphitic carbon is fatal to 
the success of either process. The presence of manganese is helpful 
here as tending to produce white iron. 

The set of curves in Fig. 14 will serve for a partial guide in the 
mixing of grades of iron for the production of any kind of castings. 
The following points must be kept in mind, however : 1st. That 
these results cannot be produced by means of silicon if any con¬ 
siderable amount of manganese, sulphur, or phosphorus is present. 
2d. It is probable that these curves would have been modified if 
iron with an average total carbon had been used, say 3.5 per cent, 
instead of 2 per cent. Silicon seems to influence the physical qual¬ 
ities of iron (a) because of its effect on the distribution of the 
carbon ; (b) because of its effect upon the iron itself. The former 
is a desirable effect, increasing strength, ductility, and softness, 
while the latter is an undesirable effect, resulting in decreased 
strength and increased hardness. In Fig. 14, evidently the in¬ 
fluence upon carbon predominates in the early part of the series ; 
i.e., from 0 per cent silicon to about 2.5 per cent, silicon, while 
the direct influence upon the iron predominates from 2.5 per cent, 
silicon to the end of the series. If the total carbon had be«?n 




* 



t 





























































\ •' 










■ 





























PHYSICAL QUALITIES OF CAST IRON. 


38 


greater, the predominance of the influence of the silicon upon the 
carhon might have extended further in the series. 

29.—In foundry practice it is desirable that a large amount of 
“ scrap ” be used ; partly because “ gates,” “ risers,” etc. are a nec¬ 
essary product of every heat, and must not be wasted, and partly 
because a good deal of scrap is offered for sale at a low price. The 
effect of remelting iron is to harden it, and therefore scrap is always 
of harder grade than the “ pig ” from which it was originally cast. 

The hardening effect of remelting is very clearly shown by some 
experiments made at the Gleiwitz foundry in Silesia, and quoted 
by M. Ferd. Gautier in a paper read before the Iron and Steel 
Institute (see Journal of 1886). The results are given in the fol¬ 
lowing table : 



Original 

Pig Iron. 

After 

4th Casting. 

After 

6th Casting. 

Graphitic carbon 

2.73 

2.54 

2.08 

Combined “ 

0.66 

0.80 

1.28 

Total 

3.39 

3.34 

3.36 

Silicon 

2.42 

1.88 

1.16 

Manganese 

1.09 

0.44 

0.36 

Sulphur 

0.04 

0.10 

0.20 

Phosphorus 

0.31 

0.30 

0.30 


It will be seen that the six successive meltings resulted in a 
decrease in the amount of silicon and manganese, and an increase 
in the amount of sulphur. (This latter probably absorbed from the 
fuel.) Graphitic carbon is decreased, and combined carbon is in¬ 
creased ; therefore the combined effect of decrease of silicon and 
increase of sulphur was greater than the effect of the decrease in 
manganese. The change necessary to convert this again into soft 
gray iron is the addition of silicon, provided the amount of sulphur 
is not too great. The reason for the hardening effect of remelting 
is (a), the reduction of the silicon, resulting in the redistribution of 
carbon ; and (b), the increase of sulphur. Of the substances which 
are found in combination with iron, silicon has the greatest affinity 
for oxygen ; manganese being next in order. Therefore, when iron 
is melted in the presence of an air blast, some of the silicon is always 



































































































































































































































































































































PHYSICAL QUALITIES OF CAST IRON. 


39 


oxidized, and usually some of the manganese. Iron is melted in 
the presence of anthracite coal or coke, and hence there is the 
possibility of absorption of sulphur. 

The “ softening ” of scrap has almost invariably been accom¬ 
plished by the addition of “ Scotch pig,” or some other grade of iron 
high in silicon, as the iron obtained from the carbonate ores of Ohio. 
Scotch pig sometimes contains a considerable amount of manganese, 
which tends to counteract the desired effect of the silicon. In some 
cases the amount of manganese is so large that the effect is to 
harden, rather than to soften iron with which it is mixed. If the 
total carbon is sufficiently high, the softening of iron can be 
accomplished very satisfactorily by the addition of a proper amount 
of ferro-silicon, which usually contains about 10 per cent, of silicon. 
But if total carbon is low, pig iron high in silicon and carbon would 
serve better, because it would carry a larger amount of carbon per 
unit of silicon. 

30.—“Burnt scrap” is cast iron which has been exposed during 
use to the action of oxygen at high temperatures ; as, for instance, 
old grate bars, salt kettles, etc. A portion of the iron becomes iron 
oxide. If such iron be melted, the iron oxide gives up its oxygen to 
the silicon, manganese, or carbon present, in obedience to the law of 
affinities ; and the results are silica and oxide of manganese, solids 
which appear as slag, and the gas CO or C0 2 . The reduction of the 
total carbon will result in harder iron, and the reduction of the 
silicon will result in the appearance of all the carbon present as 
combined carbon. This result is so very decided that a whole heat 
may “ run hard ” because of the introduction of a comparatively 
small amount of “ burnt scrap.” If the effect of burnt scrap is due 
simply to the fact, that the silicon has been removed by the oxygen 
of the iron oxide, then if it were melted together with ferro-silicon, 
the result would be gray, soft iron. But there might be iron oxide 
enough present to reduce the total carbon too much ; and then the 
silicon could not produce gray iron, because it would not have 
enough carbon to work with ; and in this case carbon would have 
to be added as well as silicon, and pig iron high in carbon and 




PHYSICAL QUALITIES OF CAST IRON. 


40 


silicon would serve better than ferro-silicon. The iron oxide which 
is seen as rust on the surface of scrap, is effective in the reduction 
of silicon, etc. upon melting. Its effect is of little importance how¬ 
ever, as it is little in amount, relatively. It must not be concluded 
from this that silicon will make good iron out of all kinds of scrap. 
Some scrap is hopeless because of the presence of sulphur or phos¬ 
phorus. It must be remembered that the addition of silicon to 
very gray iron can produce no good result, but rather the reverse ; 
because the carbon is already graphitic, and the only effect of the 
addition of silicon is its undesirable direct effect on the iron itself. 

31.—Mr. J. W. Keep, of Detroit, Michigan, has made a very 
valuable series of experiments to determine the influence of alumi¬ 
num upon cast iron (see Transactions Am. Inst. Mining Engineers, 
Vol. 18, p. 102). He shows clearly that the influence of aluminum 
upon the distribution of carbon, is similar to that of silicon ; but 
that the effect of aluminum upon the iron itself, is not an un¬ 
desirable one, as in the case of silicon. It would therefore, be a 
better material for effecting the redistribution of carbon. It is 
found, however, that there are some very serious practical diffi¬ 
culties in introducing the aluminum, either pure or as ferro-alumi- 
num, into the cast iron. 

The effect of cooling upon cast iron.—Cast iron is melted and poured 
into a mould. It takes the form of the mould and cools gradually 
to the temperature of the surrounding air. In cooling, the iron, 
of course, shrinks. The shrinkage may be divided into two parts : 
fluid shrinkage, and solid shrinkage. After being cast the fluid iron 
begins to cool, and shrinks in volume, and the fluid iron from the 
“ runners ” and “risers” runs down to supply this shrinkage, until 
the connection between them and the casting is frozen up. The 
walls of the casting are now partly solidified, but are still weak, and 
yield to the force of the shrinkage of the still fluid iron inside of 
the casting, and, if it be of large volume, depressions in the surface 
result. After a little the walls become strong enough to resist the 
force, and then, since there is no source from which to supply the 
shrinkage of the still fluid iron at the centre of the casting, there is 


















































































































































































































































































































































































































































































































* 
































PHYSICAL QUALITIES OF CAST IRON. 


41 


no resource but for it to become “ spongy.” A spongy cross section 
is necessarily weaker than one of solid iron, and is therefore un¬ 
desirable in a stress member of a machine.. The fluid shrinkage 
may be partly supplied by “ feeding from a riser ” in the way which 
is customary in foundries: Evidently the tendency to form spongy 
iron because of unsupplied fluid shrinkage, will increase with the 
volume of the casting. After the whole casting has become solid, 
its dimensions are steadily reduced till it reaches the temperature 
of the surrounding air. 

33. —When iron solidifies its structure becomes crystalline, and 
the lines of crystalization arrange themselves at right angles to the 
surface from which the flow of heat takes place. This crystaliza¬ 
tion may be represented by lines, as in Fig. 15. Along the line a b 
the crystalization lines intersect, and the structure is broken up 
and weakness results. If, however, the corner be rounded, as at c, 
and the re-entering angle be replaced by a “ lillet” as at d, the di¬ 
rection of the lines of crystalization is changed gradually, and the 
line of weakness is avoided. Whether this theory is correct or not, 
it is known practically that the line of weakness does exist, under 
the circumstances described, and that it may he avoided as sug¬ 
gested. The conclusion from this is that sharp corners and re-entering 
angles are to be avoided in the design of cast machine members. The 
rounded outlines also give a more pleasing appearance. 

34. —Experience points to the conclusion that castings of small 
cross section shrink more than those of large cross section. To test 
this conclusion, Mr. Thomas 1). West made an experiment which 
he describes in his book, “ American Foundry Practice.” He cast 
two bars 14 feet long, from the same iron, and as far as possible, made 
the conditions of casting the same for both. The cross sections 
were rectangular, one being 4"x9" and the other 4"x2". The total 
shrinkage for the larger bar was J" and for the smaller one was 1 j". 
This may possibly be explained as follows, as Mr. West suggests: 
A casting cools from the surface, and therefore during the cooling 
the surface will be the coolest part, and the heat will increase 
toward the centre. The external portions are held from their 

6 


















* 











































































































































































































































PHYSICAL QUALITIES OF CAST IRON. 


42 - 


normal shrinkage by the resistance of the hotter internal portions, 
which are not yet ready to shrink as much. This goes on till the 
surface has reached the temperature of the surrounding air and 
stops shrinking ; the hotter portions nearer the centre now try to 
shrink as they in turn cool down, but are prevented by the exter¬ 
nal part which has stopped shrinking. This action is necessarily 
greater in large castings than in small ones, and therefore the 
shrinkage is less in the larger ones. 

if this theory be correct, the internal stresses due to the shrink¬ 
age will increase with the size of the casting. Hence' it follows that 
castings having thick and thin parts attached to each other, will 
shrink unequally, and be in a state of internal stress, which renders 
them less able to withstand the action of external forces. 

Suppose it is required to put a strengthening rib B, on A, Fig. 16, 
and that it is made of the form shown : i.e., thin relatively to A, 
and having parallel sides. B would shrink more than A, and shrink¬ 
age stresses, tension in B and compression in A, would result, which 
would be concentrated along the juncture of A and B, which would 
therefore yield under a less external force. If the form shown in 
(b) were used, the shrinkage stresses would be distributed, and the 
casting would be stronger. 

35. —The lessons to be learned from these facts are as follows: 
1st. All parts of all cross sections of castings for machine members 
should be as nearly of the same thickness as possible, to avoid con¬ 
centrated shrinkage stresses, with their accompanying weakness. 
2d. If it is necessary to have thick and thin parts in the same cast¬ 
ing, change of form from one to the, other should be as gradual as 
possible. 3d. Castings should be made as thin as is consistent with 
strength, stiffness, and resistance to vibration,, to avoid the shrinkage 
stresses, and spongy metal due to the shrinkage of large masses. 4th. 
Since some shrinkage stresses always must exist in cast machine 
members, they should be taken into account in designing. 

36. —Special care should be taken in the design of wheels, because 
they are peculiarly liable to excessive shrinkage stress on account 
of their form. In a pulley the thin rim tends to shrink more than 









































































PHYSICAL QUALITIES OF CAST IRON. 


43 


the heavier arms, and the rim is thereby put in tension, and the 
arms in compression. It is not uncommon to see a rim ruptured in 
this way. If the same pulley has a relatively heavy huh, the latter 
will remain fluid until the arms and rim have solidified ; the tension 
on the rim will then force the arms into the 3 'et fluid hub, which 
in turn shrinking, will put a tensile stress on the arms. The arms 
of fly wheels tend to shrink away from the heavier rim, and are 
therefore in tension. 

37.—Effect of internal stress upon the stress-strain diagram. Suppose 
that a casting he made of the cross sectional form shown in Fig. 
16 (a). The part B tends to shrink more than A, and therefore B 
is put in tension, and A is put in compression. If there be com¬ 
pressive stress in a piece of material, and a tensile force be applied 
to it, the first effect is the neutralization of the compressive stress. 
No tensile stress can he induced in the piece until the compressive 
stress is entirely neutralized. If now a tensile force he applied to 
the casting (a) Fig. 16, it follows that no tensile stress will result 
in the part A, and therefore that all the stress will be concentrated 
on the part B. To illustrate this, suppose that a tensile force is 
applied to a rope, and that half of the strands are tight, and half 
slack. Stress will result in the strands which are tight until they are 
strained so much that the others are brought into play, and then 
the tension is sustained by the whole cross section, provided the 
strands originally tight were not broken. So in the casting : the 
part B sustains the stress until the compression in A is neutralized, and 
its tensile resistance is brought into play. Because of this the unit 
stress (stress per unit of cross sectional area sustaining the stress), 
is very great in the early part of the test, and the strain, having a 
proportionate value, is also much greater than it would be if the 
whole area of cross section sustained the stress. The stress- 
strain diagram therefore takes the form shown in Fig. 17 ; the 
initial part of the curve representing the concentration of stress on 
some fraction of the cross sectional area. If the stress had been 
gradually relieved at A the curve would have returned over AB and 
OB would be the permanent strain or “ set.” If the internal stress 



PHYSICAL QUALITIES OE CAST IRON. 


44 


in B, Fig. 16, had been sufficiently great, it might have been rup¬ 
tured before the tensile resistance of A could be brought into action. 
In any case the piece could not sustain as great external force as if 
there had been no internal stress, because there would be no time 
during the application of force when the whole area of cross section 
would offer resistance, without some part having been previously 
weakened. 











CHAPTER IV. 


Variations of the Physical Qualities of Forged Materials, 
Their Causes and Control. 

38. —There may be internal stresses in forged material, similar to 
those resulting in cast material from unequal shrinkage. They are 
usually the result of working the material too cold. To illustrate : 
Tf a thin piece of ductile material be laid on an anvil and struck 
with a hammer, the piece is made thinner, and its superficial 
dimensions are increased ; i.e., it is made longer and broader. Sup¬ 
pose now that the piece is thick instead of thin, and that it receives 
a blow as before ; the influence of the blow extends only a little 
way into the material, and the surface is made longer and broader. 
Since its extension is resisted by the part which is uninfluenced by 
the blow, the material at the surface is put in compression, and the 
inner portion in tension. The initial part of the stress-strain 
diagram would be like that shown in Fig. 17. If the working be 
done at a red heat the material is soft and weak, and therefore 
yields to the stresses introduced by the hammering or rolling, and 
the stresses are equalized. From this it follows that if there are 
internal stresses due to “cold working” in a piece, they will be 
relieved by heating the piece to redness and then allowing it to cool 
slowly. This is annealing to relieve internal stress. 

39. Effect of lack of homogeneousness of material on the stress-strain 
diagram. In the manufacture of wrought iron the elements of the 
piles of “ muck bar ” or scrap, are drawn out in rolling into long 
lines of crystals, which are separated by more or less slag or oxide 
of iron. Because of this, wrought iron seems to have a fibrous 














PHYSICAL QUALITIES OF FORCED MATERIALS. 


46 


structure. Since the pile is sometimes made up of bars or scrap, of 
entirely different quality, the structure may lack homogeneousness. 
This has a tendency to modify the form of the stress-strain dia¬ 
gram. Suppose, for example, that a test piece of wrought iron has 
half of its area of cross section of a material whose elastic limit is 
at E', Fig. 18, and that the other half of the cross section is of 
material whose elastic limit is at E. Let a constantly increasing 
tensile stress be produced in this test piece. When the stress 
reaches the value represented by the ordinate of E, the weaker part 
of the material begins to yield more rapidly, and the unit stress on 
the stronger part is very greatly increased, its elastic limit is ex- • 
ceeded, it also yields, and the curve takes the form shown, 
running parallel to the axis of X, or nearly so, until the stress is 
again distributed over the entire surface of the cross section ; after 
which the curve rises continuously until the maximum stress is 
reached. 

40.—Effect of heat treatment on the carbon, and on the structure 
of ingot iron and steel. The carbon which has heretofore been 
spoken of as in combination with iron, may exist in two forms. 
Hardened steel treated with cold, dilute hydrochloric acid, is taken 
completely into solution ; whereas annealed steel leaves a carbon¬ 
aceous residue when similarly treated. The carbon in hardened 
steel will be called hardening carbon and the carbon in annealed steel 
will be called non-hardening carbon ; the temperature of the air will 
be called T ; the temperature at which red just shows in the dark, 
will be called V : the temperature of full redness, will be called W ; 
and the temperature at which the edges of steel just begin to melt, 
will be called M. 

Suppose a piece of annealed steel to be gradually heated from T 
to M. Certain changes occur in the carbon, and in the structure of 
the steel, which will be represented graphically. In Fig. 19, A, C, 
and E represent carbon change, and B, D, and F represent struc¬ 
ture change. Temperature change is measured vertically, and 
change of time is measured horizontally ; therefore an inclined 
line, like A, indicates a temperature change upward, which 








































































































































































/ 












































































































































































































. 




















































































‘ 
























^Ill'll ill I! 




































































PHYSICAL QUALITIES OF FORGED MATERIALS. 


47 


occupies some appreciable time ; i.e ., slow heating; while an in¬ 
clined line like C, indicates a gradual temperature change down¬ 
ward ; i.e., slow cooling; and a vertical line like E, indicates 
instantaneous cooling, or “quenching.” 

The length of the short horizontal lines of B, D, and F indicates, 
conventionally, the size of the crystalline structure of the steel. In 
A, C, etc., dotted lines indicate non-hardening carbon, and full, 
heavy lines indicate hardening carbon. A show's that as the 
temperature of the annealed steel is gradually raised, the carbon 
remains non-hardening carbon till a temperature of full redness is 
reached, when it all turns to hardening carbon. This change of 
carbon at \\ r is an instantaneous change. B show r s that the crystal¬ 
line structure remains the same as that of the annealed steel (the 
size of which depends on previous heat and mechanical treatment), 
till W is reached, when it becomes much reduced. This change is 
also instantaneous, and the structure becomes exceedingly tine, 
almost amorphous. This is the structure which corresponds to 
the greatest ductility, toughness, and shock resisting power of the 
material ; and which is therefore best in wrought machine mem¬ 
bers. From W on, with increase of temperature, the structure 
grows constantly coarser, and the steel more brittle and less tough, 
till M is reached. 

If this steel he cooled slowly to T, the changes which occur are 
shown by C and 1). The carbon does not change till a temperature 
just above V is reached, when it tends to change back to non-harden¬ 
ing carbon. This change occurs slowly, and the slow cooling allows 
it to become complete. No change of structure occurs during this 
slow cooling, but the coarse structure due to heating to M is re¬ 
tained. 

If the cooling from M had been by quenching, the results would 
be indicated by E and F. The sudden cooling does not give time 
for the hardening carbon to change back to non-hardening carbon, 
and it is therefore retained, and the steel is hardened. The result 
then of slow cooling from M, is to produce soft, coarse, and hence 
brittle steel ; while the result of quenching from M, is to produce 






PHYSICAL QUALITIES OF FORGED MATERIALS. 


48 


hard, coarse, and hence brittle steel. No method of cooling from M 
can produce fine structure. The same would have been true if the 
steel had been raised to any temperature between W and M ; the 
structure corresponding to the temperature would have been re¬ 
tained regardless of the method of cooling. If either the product of 
Cl) or of EF he reheated, it retains its coarse structure till W is 
reached, and then again becomes instantly amorphous, as shown in 
(I. The steel, which was made brittle and coarse by overheating, 
is restored by simply heating again to W. This restoration, how¬ 
ever, is never perfect, probably because of the iron oxide which has 
formed on the surface. 

If a piece of annealed steel be heated to W, and quenched, it 
will be exceedingly hard, and the structure will be as fine as pos¬ 
sible, because quenching, if the piece be small enough so that the 
cooling can be practically instantaneous, prevents change either of 
carbon, or of structure, and both are held just as they are at W. 
The material is then in the best possible condition for hardened 
steel. See diagrams H and 1. If the piece of tool steel be heated 
to W and allowed to cool slowly, the changes which take place are 
represented by diagrams J and K. The carbon changes back to 
non-hardening carbon, and the structure changes back to that of 
the annealed steel. The structure changes occurs between W and 
V, and not below V. The structure changes are a function of time, 
and if the heating in B were more gradual, a still coarser structure 
would be attained at M. In K if the cooling were effected more 
quickly, the structure would not attain the coarseness of the an¬ 
nealed steel. 

No carbon change occurs above a point just above V. The 
tendency to change hardening carbon to non-hardening carbon is 
probably strong at all temperatures below that of dark redness, and 
in the case of hardened steel it is held from being operative by the 
sudden cooling, because this cooling renders the materials more 
resistant to the tendency to change of carbon. If, however, a piece 
of steel which has been hardened, be slowly heated, it is found that 
the tendency to change becomes operative at a temperature very 






I - 

-t: 



e f a 


































































































































PHYSICAL QUALITIES OF FORGED MATERIALS. 


49 


much below V. Thus, if it be heated to a temperature correspond¬ 
ing to the formation of straw color .oxide, there will be very per¬ 
ceptible softening of the steel. If then steel be heated to W, and 
cooled by quenching to V, and then be allowed to cool slowly, the 
fine structure will be retained, and the hardening carbon will have 
had opportunity to change back to non-hardening carbon, and the 
material will be soft and tough. This method was applied with 
great success to the toughening of car axles, by Mr. John Coffin at 
the Cambria Iron and Steel Works, at Johnstown, Pa. 

If steel be melted, and quenched from the fluid state, the carbon 
will be all hardening carbon, and the structure will be exceedingly 
fine. But if it be allowed to solidify, and then be cooled by quench¬ 
ing, the carbon will be hardening cai 4 >on, and the structure will be 
coarse. If it be allowed to solidify and then to cool slowly, the 
carbon will be non-hardening carbon, and the structure will be 
coarse. These facts have been proved, and apply to the annealing 
of steel castings. There has been a very general impression that 
very slow cooling of steel castings after solidification would result in 
toughening and softening them. The above facts, however, lead to 
the conclusion that such heat treatment would result in softness and 
brittleness ; and experience proves this conclusion. But if they be 
allowed to cool to V or below, and then be raised again to W and 
quickly cooled to V, and then allowed to cool slowly through the 
rest of the temperature range, they will be soft, fine grained, and 
tough. In large castings an approximation to this heat treatment 
was attained by Coffin,' by allowing the casting to cool to, or below 
V, and then placing it in a re-heating furnace where the tempera¬ 
ture was raised to W. The fires were then drawn, the furnace 
doors were opened, and the casting was cooled as rapidly as pos¬ 
sible by the admission of cold air till V was reached, and then the 
furnace was closed, and the casting was allowed to come slowly to 
the temperature of the air. 

41 —On the effect of mechanical working upon structure. If steel 
be heated to a white heat, the coarse structure corresponding to 
this heat, may be broken up and rendered fine by'mechanical work- 
7 



PHYSICAL QUALITIES OF FORGED MATERIALS. 


50 


ing, as rolling or hammering. Steel which is to he worked may 
therefore be heated above W, and still be of fine grain if the work¬ 
ing does not cease while the temperature is yet above W. If the 
steel is worked at a temperature very much below W, there is a 
tendency to introduce stress by “ cold working ” as previously ex¬ 
plained. Also steel is particularly brittle at what is usually called 
u blue heat ” (430° to 600° F.), and if it he worked at this heat the 
brittleness remains on cooling. It is, however, removed by anneal¬ 
ing. It is not possible to work large forgings so that there 
shall be a uniformly fine structure and no internal stress, because 
if forging ceases in any portion while the temperature is very much 
above \V, the structure becomes coarse, and if forging continues till 
the iron is black, internal stress is introduced ; therefore this result 
should be accomplished by subsequent heat treatment. 

42.—Annealing. By annealing is usually understood the process 
of heating to full redness, or above, and cooling very slowly by 
burying in ashes, or powdered lime or charcoal. The objects of an¬ 
nealing are : • 

1st. To relieve internal stress. 

2d. To refine, i.e ., to render the structure fine in grain. 

3d. To change the carbon from hardening carbon to non-harden¬ 
ing carbon. 

Internal stresses are relieved by heating to redness. If it is 
required to anneal a forging which is to become\a machine stress 
member, it should be accomplished as follows : After forging, the 
piece should be allowed to cool to V, or below ; its temperature 
should he then slowly, and uniformly, raised to W ; it should then 
be quenched to V, and allowed to cool slowly in the air. The heat¬ 
ing relieves any internal stresses ; quenching from W to V fixes the 
fine structure, and confers toughness; cooling slowly from V affords 
opportunity for hardening carbon to change to non-hardening 
carbon, and therefore confers softness. The forging is therefore in 
the best condition to resist stress, and for working in the machine 

shop. • 

If annealing is required simply to confer softness, and the piece 



PHYSICAL QUALITIES OF FORGED MATERIALS. 51 

is to be subjected to subsequent heat treatment, as for instance, the 
steel which is annealed for working into cutters, which are after¬ 
wards to be hardened, it is only necessary to heat the piece to W 
and bury it in lime, ashes, or charcoal until it cools. The structure 
will be coarse, but it will be refined again by hardening. 

43.—Hardening and Tempering. Steel may be hardened by quench¬ 
ing from any temperature above W, but the higher the temperature 
the coarser the structure, and the more brittle the hardened piece. 
If brittleness is objectionable, as it usually is, the hardening should 
be accomplished by quenching from the lowest temperature at 
which hardness is conferred : i.e ., from W. For most purposes the 
steel so hardened is still too brittle, and will not hold a thin 
cutting edge, and something of hardness is sacrificed to gain 
greater toughness, by means of the process of tempering, as fol¬ 
lows : After quenching from W, the piece is slowly raised to 
a temperature at which the colored oxides begin to form on a 
polished surface of the piece. This softens and toughens the 
piece, probably by allowing some of the hardening carbon to 
change to non-hardening carbon. When the temperature cor¬ 
responding to the required degree of softness’ is reached, the source 
of heat is removed, and the piece is allowed to cool again to the 
temperature of the air. 

There is a strong tendency for “ high carbon ” steel to crack in 
hardening. This is, of course, partly due to the fact that all parts 
cannot be cooled at the same instant, or at the same rate. Thin 
parts will cool more quickly than thick parts.; external portions 
will be cooled first, and internal portions afterward. This will 
result in unequal shrinkage and severe internal stress, just as in the 
case of castings. But ingot, or weld iron, will not crack under the 
same conditions of cooling which would cause high carbon steel to 
crack. The reason for this is two fold : 1st, the high carbon steel is 
more brittle than the iron ; and 2d, it has a greater coefficient of 
expansion. Therefore the effect of the unequal shrinkage is to 
produce more severe stress, and it is less able to withstand this 
stress. It will be evident, therefore, that great care should be taken 


* 


















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* 




i 




f r 























































. 

* 



. 
























. • 




































. 





































PHYSICAL QUALITIES OF FORGED MATERIALS. 52 

in the design of parts which are to he hardened. As in castings, all 
sections should be as nearly as possible of the same thickness, and 
all large masses should be avoided, as well as all sharp internal 
angles. As great surface as possible should be exposed to the action 
of the cooling medium. These precautions will insure an approxi¬ 
mation to uniform cooling, and reduced quenching stress, and less 
tendency to crack will result. 

When a thin part is necessarily attached to a thick part, it is 
sometimes possible to fasten another piece of metal in contact with 
the thin part during heating and quenching. The thin part has its 
thickness virtually increased thereby, so that, if the attached piece 
be of the right dimensions, the thin part will be cooled at the same 
rate as the thick part, and quenching stress is thereby avoided. 

44. —Case Hardening. A machine part of wrought material some¬ 
times needs to be ductile and strong in order to resist stress, and at 
the same time needs to have a hard surface to resist wear. This 
result is accomplished by “case hardening” weld or ingot iron. 
Pieces to be case hardened are packed in an iron box, where they 
are surrounded by carbon in the form of “ bone black ” or animal. 
charcoal ; the box is sealed, placed in a furnace, and raised to a 
temperature of full redness ; this temperature is maintained from 
three to twenty-four hours. The pieces are then taken from the box 
and dropped into water while yet red hot. During the process the 
surface of the pieces has been converted into steel by the absorp¬ 
tion of carbon, and this steel surface has been hardened by the 
quenching. The core or inside portion, however, remains ductile’ 
iron, and is not hardened. The surfaces of case hardened pieces 
must be finished by grinding. Case hardened pieces may be treated 
in exactly the same way as high carbon steel : i.e ., the surface may 
be softened by annealing ; it may be rehardened by quenching 
again from W ,; and it may be tempered. The inner part is un¬ 
affected by this treatment, and remains ductile. 

45. -Effect of foreign substances upon ingot iron and steel. Experi¬ 
ments show that the introduction of silicon into molten steel some¬ 
times seems to strengthen the product and make it less ductile, i.e., 


















































































































PHYSICAL QUALITIES OF FORGED MATERIALS. 


53 


to make brittle ; while at other times it seems to strengthen and 
make more ductile, i.e., to toughen. This may probably be 
accounted for as follows : Silicon introduced into molten steel has 
two tendencies : 1st, to combine with any oxygen present, whether 
free or combined with iron as FeO, to form silica, which is fluxed 
off by FeO, or oxide of manganese. Perhaps, also, it acts to prevent 
the formation of gas, which would result in spongy sections and 
weakness. ‘2d, to combine directly with the iron itself. 

The effect of the first would undoubtedly be to increase strength 
and ductility ; but the silicon which has caused this change is 
found in the slag, and not in combination with the iron, and there¬ 
fore the change cannot be said to result from the introduction of 
silicon into iron, if too much silicon were introduced for the removal 
of oxygen, the excess would combine with the iron itself, and it 
seems probable that it would cause loss of ductility, and increase of 
brittleness. 

Manganese, like silicon, when added to molten steel removes iron 
oxide, and tends to prevent the formation of blowholes. The 
manganese which is useful for this, however, as in the case of silicon, 
appears in the slag, and not in combination with the steel ; its effect 
so far is, therefore to increase tensile strength and ductility, and 
hence to reduce brittleness. The manganese which is com¬ 
bined with the steel increases tensile strength and hardness, 
while it probably reduces ductility ; this reduction of ductility is 
less than that due to any of the other hardening, strengthening 
substances. When the amount of manganese is as high as 1.5 to 
2.5 per cent, the steel is very brittle. If, however, the amount be 
increased till it exceeds 7 per cent., the brittleness disappears, and 
the material is very tough, and so hard that it*is used for cutting 
tools. These manganese special steels contain- from 8 to 20 per 
cent. Mn. Manganese is thought to counteract the “ red shortness ” 
caused by the presence of sulphur. 

Sulphur and phosphorus both tend to harden and strengthen the 
steel with which they are combined, and to reduce ductility. Sul¬ 
phur causes red shortness, brittleness when red hot; and phosphorus 











♦ 





































V 


A 

































% 
























































































PHYSICAL QUALITIES OF FORGED MATERIALS. 


54 


causes cold shortness, brittleness when cold. Phosphorus seems to 
have little power to produce these effects in steel, which is very low 
in carbon, say less than 0.1 percent. 

Chromium combined with steel seems to increase the intensity of 
the hardening effect due to the carbon present. The special steel 
known fts “chrome steel,” is used for tools, and is more readily forged 
than manganese or tungsten steel. 

Tungsten steel contains from 2 to 11 per cent, of tungsten. It is 
used as a special steel for tools, under the names “ Mushet’s steel,” 
“crescent hardened steel,” etc. It is intensely hard, of high tensile 
strength, and very brittle ; it is forged with great,difficulty, and 
only at a red heat. 

The effect of aluminum upon wrought iron and steel ‘ castings has 
been experimentally investigated by Mr. .J. \V. Keep (Trans. Am. 
Inst. Mining Engineers, vol. xviii., page 835). One series of experi¬ 
ments seem to' indicate that successive additions of aluminum, up 
to about 2.5 percent., to ingot iron, with total carbon about 0.3 per 
cent., showed decided increase in ultimate strength and elastic 
limit, with perhaps slight increase in ductility ; hardness was 
reduced. Another series seems to indicate that successive ad¬ 
ditions of aluminum up to about 2.5 per cent.,.to steel castings with 
average total carbon 1.34 per cent., resulted in decidedly increased 
strength, elastic limit, and ductility ; hardness was much increased. 
The effect of the aluminum on the molten metal is to increase 
fluidity ; but whether this results from reduction of melting point, 
or increased heat, does not seem to be clear. The aluminum also, 
like silicon and manganese, tends to prevent the porosity resulting 
from occluded gas. 

It is found that the addition of nickel to steel produces decided 
changes upon its physical qualities. Metallic nickel may be ad¬ 
ded to the molten steel in the open hearth furnace, and iron takes 
it into solution, or combination in all proportions, at least up to 
20 per cent. The nickel seems to increase elastic limit, ductility, 
and hardness. This of course greatly increases its shock resisting 
power, and nickel steel is being introduced quite extensively in 




PHYSICAL QUALITIES OF FORGED MATERIALS. 


55 


armor plates. The hardness seems to be a result of the combined 
effect of nickel and carbon. An analysis of one armor plate gives 
carbon 0.88 per cent., manganese 1.1 per cent., nickel 2.5 per cent. 

46.—On the physical effects of mal-treatment of materials. If a test 
piece of ductile material be strained beyond its elastic limit, it will 
be found on the relief of stress, that the character of the ma¬ 
terial is greatly changed ; for, if after a short interval of rest, 
it be tested‘again, its elastic limit and elastic resilience will be 
higher, its tensile strength will be greater, and its ductility and 
ultimate resilience will be less. The modulus of elasticity will 
be but slightly changed, if at all. By straining this piece, 
then, the “elastic range ” has been increased, the piece is made 
stronger and better able to resist shocks within the elastic limit, 
but less ductile, and less able to resist shocks exceeding the 
elastic limit. These changes are shown graphically in Fig. 
20. The stress-strain diagram OGKLMN is such as would 
usually result from a test of a ductile material, like ingot or 
weld iron. On reaching some point, as K, stress is gradually 
relieved, and the curve descends to the X axis at A. On reap¬ 
plication of tensile force the curve rises along the line AF nearly 
parallel to OG. The elastic limit is now at F, a point much higher 
than the original elastic limit G. The curve then continues, a 
little higher than it would if the stress had not been discontinued 
at K, until the maximum is reached at E.* 

If the force could have been instantly reapplied at A, the line 
FED would probably have coincided with LMN, because the change 
is a function of the time of resting, after relief of stress. The diagram 
OGKLMN may be considered the stress-strain diagram of one 
material, while AFPED is the stress-strain diagram of another 
material. It is as if a new test began at A. Let a represent the 

* That the maximum strength is increased, has been demonstrated by Baus- 
chinger. He first broke a long test piece by tensile force. It was of uniform 
cross section, and hence all of its parts must have been strained well past the 
elastic limit. He then broke one of the pieces and found increased strength. 
This was repeated six times, and each repetition resulted in increased strength. 







\-\gZO 














































PHYSICAL QUALITIES OF FORGED MATERIALS. 56 

first diagram, and b the second. The elastic range of b, represented 
by AF, is greater than that of a, represented by OG. The.elastic 
resilience of b, represented by the area AFJ, is greater than that of 
a, represented by OGH. Experiment has proved that the points E 
and D are not changed in their relation to the axis of V, by the 
relief of stress ; and therefore the ductility of a , represented by OG, 
is greater than the ductility of 5, represented bf AC. The ultimate 
resilience, proportional to the total area under the stress-strain 
curve, is evidently greater in a than in b. AF is nearly parallel to 
OG, and hence rigidity is nearly the same for both. 

If, instead of the almost immediate reapplication of force, a con¬ 
siderable interval of rest had been allowed, say twenty-four hours, 
the elastic limit, and ultimate strength would have been still further 
raised, and the diagram would be like Fig. 21. If stress were not 
discontinued till the maximum had been nearly reached, the 
strained material would resemble a very brittle material. 

It may be stated as a conclusion warranted by experiment (see 
Trans. Am. Soc. Civil Engineers, vol. xxiv., page. 159), that stress of 
any character, which strains a ductile material beyond its elastic 
limit, will render it harder, and stronger, and less ductile in resist¬ 
ing stress of any other character. Annealing removes these effects 
almost completely. The process of “cold rolling” by which shaft¬ 
ing is produced, illustrates the alterations of the qualities of ductile 
material due to straining beyond the elastic limit. In this process 
iron is passed cold through highly finished rolls, under intense 
pressure. The rolled piece has its length increased, and its cross 
section reduced, and therefore, since the material takes a “set” it 
must be strained by the treatment past its elastic limit. 

Professor Thurston made *a series of tests to determine the effect 
of cold rolling upon iron. His experiments show that there results 
from the process (a), an increase in tensile strength of from 25 to 
40 per cent.; (b), an elevation of the elastic limit of from 80 to 125 
per cent.; (c), an increase of elastic resilience of from 300 to 400 
per cent.; and (d), a decrease in ductility of about 75 per cent.; a 
decrease of ultimate resilience of about 40 per cent. If, therefore, 














































. 



















































































PHYSICAL QUALITIES OF FORGED MATERIALS. 


0 / 


the product of the process is required to withstand stress (and 
especially shock), which can not exceed the elastic limit, it is far 
better than the untreated iron ; but if there is a possibility of shock 
exceeding the elastic limit, the unrolled iron might be better. 

The process of “ wire drawing,” i.e., reducing the size of wire 
with increased length by drawing cold through dies, produces the 
same result as cold rolling ; the wire requiring frequent annealing 
to restore ductility. 

47.—The effects of repeated stress on materials. Between the years 
1859 and 1870, A. Wohler planned and executed a series of ex¬ 
periments for the Prussian government, to determine the laws 
governing the behavior of metals under repeated stress. By means 
of his machines, forces of known value producing tensile, com¬ 
pressive, torsional, or transverse stress could be applied with in¬ 
definite repetition, until either rupture occurred, or it was considered 
proved that indefinite repetition of stress could not produce rupture. 
He formulated a law from the experimental work, which in sub¬ 
stance is as follows : Material may be broken by repeated application 
of a force , which would fail to produce rupture by a single application. 
The breaking is a function of range of stress; and as the recurring 
stress increases , the range necessary to produce rupture decreases. 
If the stress be reversed , the range equals the sum . of positive and 
negative stress. 

The experimental work of Wohler has been amplified and sup¬ 
plemented by the very careful work of Professor Bauschinger of 
Munich. It is found that if the results of the experiments, in which 
the repetitions of stress exceeded five million, be taken, and the 
minimum stress, and range of stress be plotted with reference to rect¬ 
angular axes, the points located fall upon a smooth curve. Fig. 22 
shows four such curves drawn from the results of Bauschinger’s 
experiments. A and B are for weld iron, and C and D for ingot 
iron. The minimum stress is measured on the axis of X, and the 
range of stress is measured on the axis of Y. Each curve has its 
own vertical scale, hut the horizontal scale is common to all. 
Where the curve comes to the axis of X the value of Y, equal to the 
8 















































' 































PHYSICAL QUALITIES OF FORGED MATERIALS. 


58 


range of stress, becomes zero, and therefore the value of X represents 
the static strength of the material; i.e ., the load the material would 
just endure continuously without rupture. 

To illustrate, suppose that a certain weld iron will just endure a 
unit static stress of 50,000 lbs. It is required to subject it to a 
minimum unit stress of— 10,000 lbs., indefinitely repeated, and 
the allowable range is required. This iron is represented by curve 
A, and when the value of X — — 10,000, the value of Y, or the 
required range, - 31,200. The maximum tension then would be 
81,200—10,000—21,200. Or suppose that a certain ingot iron will 
just endure a unit static stress of 65,000, and it is required to subject 
it to indefinitely recurring stress whose minimum value is 20,000. 
The range and corresponding maximum stress are required. On 
the curve C, which represents this material, where X 20,000, Y= 
28,000 -required range. The maximum tension- 20,000+28,000- 
48,000. 

If the static strength of a material is such that no one of the 
curves represents fit, a curve may be drawn for it nearly parallel to 
that to which it falls nearest, and the approximate results may be 
read off from it. 

Bauschinger draws the following conclusions from his experi¬ 
mental work : 

1st. “ With repeated tensile stresses, whose lower limit was zero, 
and whose upper limit was near the original elastic limit, rupture 
did not occur with from 5 to 16 million repetitions.” He cautions 
the designer that (a), this will not hold for defective material, i.e., 
a factor of safety must still be used for this reason ; and (b), that 
the elastic limit of the material must be carefully determined, 
because it may have been artificially raised by cold working, in 
which case it does not accurately represent the material. This 
original elastic limit may be determined by testing a piece of the 
material after careful annealing. 

2d. “With often repeated stresses, varying between zero and an 
upper stress which is in the neighborhood of, or above the original 
elastic limit, the latter is raised even above, often far above, the 











t 
































































































































































































' • 

• 























































•i 




. • H ' - ' > 






* 










PHYSICAL QUALITIES OF FORGED MATERIALS. 


59 


upper limit of stress, and it is raised higher, as the number of 
repetitions of stress increases, without, however, a known limiting 
value, L, being exceeded.” 

3d. “ Repeated stresses, between zero and an upper limit below 
L do not cause rupture ; but if the upper limit is above L, rupture 
will occur after a limited number of repetitions.” 

From this it will be clear that keeping within the original 
elastic limit , insures safety against rupture from repeated stress, if 
the stress is not reversed ; and that when the stress is reversed the 
total range should not exceed the original elastic range of the 
material. 

48.—Factors of Safety. The range of repeated stress can be de¬ 
termined from the method of Fig. 22, and if repeated stress were 
the only possible cause for failure, the value would be a safe one. 
But failure of a machine stress member may result not only from 

(a) Repeated stress, but also from 

(b) Flaws, or other imperfections in the material ; 

(c) Internal stresses; 

(d) Unhomogeneous material; 

(e) Shocks; 

(f) Stresses which cannot be estimated. 

To cover all these a factor of safety is usually used: i.e., the 
working unit stress is equal to the ultimate unit strength of the 
material, divided by a number which is called the factor of safety. 

Materials are so various in their qualities, and the conditions to 
which they are subjected as machine stress members are so differ¬ 
ent, that it is impossible to give any value for a factor of safety to 
cover all cases. Such a value would, indeed, be a “ factor of ignor¬ 
ance.” But if the value of the factor be decided upon, after a care¬ 
ful study of all conditions, it becomes a factor of wisdom. 

If a ductile material is to be subjected to repeated stress, whose 
minimum value is given, the range of stress and corresponding 
maximum stress^ P, which shall insure against rupture from repeti¬ 
tion of stress, may be found. Suppose the history of the manufac¬ 
ture of the material to be known ; and that imperfections are very 

































































































































































































































































































































































































































































. 


















♦ 








PHYSICAL QUALITIES OF FORGED MATERIALS. 


60 


carefully guarded against; that annealing is well done ; that the 
material is ingot metal, and hence very probably homogeneous ; 
that it cannot receive shocks in use ; and that there are no uncer¬ 
tain stresses. The probability is strongly against failure under the 
stress P, and the factor of safety should be such as would give a 
working stress a little less than P. 

This value would increase with uncertainty about the material, 
with the possibility of shocks, and with the existence of stresses of 
unknown magnitude. 

In unresilient or brittle materials, like cast iron, the factor of 
safety needs to be selected with still greater care. A brittle material 
breaks without obvious yielding ; it gives no warning, and hence 
the failure is unexpected, and its results are more apt to be serious. 

Shrinkage stresses are always present in cast iron, and a factor 
of safety is needed to guard against their weakening effect. But the 
intensity of the shrinkage stresses varies with the size and form of 
the cast member, and with the conditions of casting ; and hence 
the determination of the factor is again referred to the judgment of 
the designer. Cast iron being an unresilient material, must have 
large excess of strength when necessarily subjected to shocks. The 
excess of strength, i.e., the value of the factor of safety, depends 
upon the character and frequency of the shocks, and must be de¬ 
cided on for each special case. 

A cast iron member might be of such form that it would neces¬ 
sarily have severe shrinkage stress, and spongy sections, and be 
subjected to frequent shocks. There would be need of a factor of 
safety for each of these reasons. Suppose that the factor for shrink¬ 
age stresses is 4, for spongy sections is 1.5, and for shock resistance 
is 6. Then the total factor for the case^4X 1.5X6=36. Or it 
might be possible to make such a design that the probability of 
shrinkage stress and spongy sections would be reduced to a mini¬ 
mum, the member being still subject to frequent shock ; and factors 
1.5 and 6, giving a total factor of 9, would probably serve. 

No table of factors of safety can replace trained judgment. A 
man cannot design a good machine out of a book ; some books may 





PHYSICAL QUALITIES OF FORGED MATERIALS. 


01 


help him a little, but the good machine, if it comes at all, is a pro¬ 
duct of his trained judgment. 

49.—So-called Crystallization from Repeated Stress or Shock. Machine 
members exposed to repeated stress or shock, less than could cause 
rupture according to Wohler’s law, sometimes yield after a long 
time to a very much less stress or shock than they had previously 
endured safely. The fracture in such . cases is often very coarsely 
crystalline, and it has often been supposed that the repeated stress 
has caused a change of molecular structure, or crystallization, as it 
is called. Coffin explained this as follows : If material is broken by a 
single application of a load equal to its ultimate strength, it is torn 
apart, and does not separate along the surfaces of the natural 
crystals of the material. But if a stress member be supposed to 
have a very small flaw in some section, repeated stress tends to 
increase it gradually, and it spreads along the surfaces of the natural 
crystals of the material, until it has become so large, and the section 
is so much reduced, that it yields under a stress or shock far less 
than those previously resisted. The fracture shows the real 
structure of the material. Many cases of this kind may result from 
coarse crystalline structure due to improper heat treatment. 












































































































































































































































































































CHAPTER V. 


Alloys. 


50. —It has been explained that iron unites with the substances 
carbon, manganese, silicon, sulphur, phosphorus, chromium, tung¬ 
sten, aluminum, and nickel ; and that the' resulting mixtures have 
certain physical qualities due to the union. These are alloys , al¬ 
though not usually called so. It is found that nearly all of the 
metals used by the engineer, will unite with each other in certain 
proportions, many of them in all proportions, and that the alloys 
so produced have physical qualities which differ from those of either 
of their constituents. 

Whether the alloying is simply a mixture, or whether chemical 
union takes place, or whether one metal takes the other into solu¬ 
tion, is not at all clear. Possibly each occurs under certain condi¬ 
tions. The alloys of greatest importance to the engineer are the 
copper alloys, i.c., the combinations of copper with some one or 
more other metals, in varying proportions. 

Alloys of copper and tin are usually called Bronze. 

Alloys of copper and zinc are usually called Brass. 

Alloys of copper , tin , and zinc have been named by Dr. Thurston 
Kalclioids. 

51. —If successively increasing amounts of tin be added to pure 
copper, it is found that certain changes occur in color, strength, and 
ductility. The changes in strength and ductility may, be repre¬ 
sented graphically. The curves in Fig. 23 are plotted from the very 
complete experiments of Dr. Thurston (see Text-Book of the Mater¬ 
ials of Construction, page 451). From these curves it appears that 















































* 














































































































ALLOYS. 


63 


as the amount of tin is increased, the strength increases until tin 
18 per cent., copper 82 per cent, is reached ; from this point to tin 
32 per cent., copper 68 per cent., the strength falls off very rapidly ; 
and the alloy remains weak through the rest of the range. The 
ductility rises from tin 0, copper 100, to tin 4, copper 96, and then 
falls to zero at tin 22, copper 78. The ductility rises again near 
the tin end of the range to a very high value. It will be seen from 
the curves that the only part of the range where strength and duc¬ 
tility are both high, and where resilience is therefore also high, is 
between tin 10, copper 90, and tin 0, copper 100. In practice “gun 
bronze” is practically the only bronze used for machine parts. Its 
composition varies but little from tin 10, copper 90. 

The increasing strength, resulting from increased proportion of 
tin, is accompanied by increasing hardness and decreased coefficient 
of friction : i.e., it has become a better material for journal hearings. 
The alloy from copper 70 to copper 10 is evidently a very brittle 
material. But from copper 10 to copper 0, the high ductility and 
low strength, show a resilient, weak material. The coefficient of 
friction is, however, less even than that of the alloys at the other 
end of the range, and it is therefore a good material for journal 
bearings, and slides : but it is so weak that it has to be enclosed in 
shells of stronger material : i.e., it is used as a lining for brass or 
cast iron journal boxes. A small amount of antimony added to 
this gives the alloy known as Babbitt metal. Tin 33, copper 67, 
gives an alloy, which, while it is evidently exceedingly brittle, yet is 
susceptible of a very high polish, and is used for the metallic mirrors 
in certain optical instruments. It is called speculum metal. Tin 
23, copper 77 is a strong alloy, lacking in ductility, which, because 
of its sonorousness, is used for bells. It is called “ bell metal.” 

In proceeding from the copper to the tin end of the range the 
color changes, first, from the color of pure copper, to a yellow at 
copper 80, turning to gray at copper 70, and changing gradually 
to tin color during progress toward copper 0. 

52.—-Fig. 24 shows curves of strength and ductility of the brasses, 
or copper-zinc alloys. These are also drawn from the results of Dr. 




/ 


r 























































































































































































































































































































































































































ALLOYS. 


64 


Thurston’s experiments (see Text-Book of the Materials of Con¬ 
struction, page 461). Inspection of these curves shows that the 
copper-zinc mixture offers a much wider range of alloys useful to 
the engineer than the copper-tin mixture ; the range, both of high 
strength and high ductility, being much greater in the former. The 
addition of zinc to copper has an effect similar to that of the addition 
of tin to copper. The maximum effect is greater in the case of zinc, 
but it requires a greater percentage of the zinc to produce it. The 
color changes are similar to those in the copper-tin mixture. There 
is no return of ductility at the zinc end of the range, and hence 
the white alloys of copper and zinc are seldom used. The curves 
may be used to indicate proportions in mixing bronzes or brasses 
for any special duty requiring strength, ductility, and resilience. 

Dr. Thurston made a very full and careful series of experiments 
on the kalchoids, or ternary alloys of copper, tin, and zinc. He 
represented the whole field of possible combinations of the three 
metals by a certain equilateral triangular area. Many points at 
equal distances from each other were located in this area, and each 
represented an alloy with certain proportions of the three con¬ 
stituents. Alloys were made corresponding to each point, and 
tested. At the point was erected a piece of wire whose height 
represented the strength of the alloy represented by the point. 
Plastic material was then filled in between the wires, and its surface 
was moulded so that the points of the wires just showed through. 
This surface represented topographically the varying strength of all 
possible mixtures of copper, tin, and zinc, and the alloy of maximum 
strength was thereby located. (See Text-Book of the Materials of 
Construction, page 466.) 

53.—Three other alloys of copper require attention : Phosphor 
bronze , manganese bronze , and aluminum bronze . 

When any alloy containing a high percentage of copper is melted 
in contact with the air there is a strong tendency to form copper 
oxide, the affinity of copper for oxygen being exceedingly strong. 
If the alloy cools mixed with copper oxide, it is weak and brittle, 
just as iron containing iron oxide is weak and brittle. Copper 























































* 




















































































3 


























- 
























































































































































































































































































































































































































































ALLOYS. 


65 


alloys are usually melted with charcoal upon the surface to prevent 
oxidation, but the prevention is not complete. If phosphorus be 
added to the alloy just before pouring, the copper oxide is reduced 
and phosphoric acid is formed, i.e ., the alloy is purified by the 
fluxing action of the phosphorus. This increases both the strength 
and ductility of the alloy. If an excess of phosphorus be added, 
part of it may combine with the alloy and increase its strength and 
ductility ; but it is probable that the chief value of its presence is to 
prevent the formation of oxide of copper during remelting. 

Manganese bronze is made either by fusing together (a) copper 
and black oxide of manganese, or (b) copper or bronze and ferro¬ 
manganese. In the first case the product is an alloy of copper and 
manganese, and in the second an alloy of copper, manganese, and 
iron, or copper, tin, manganese, and iron. Some of the manganese 
is effective in removing, or preventing the formation, of oxide of 
copper, while the remainder combines with the copper or bronze 
to give it very greatly increased strength, ductility, and toughness. 
A manganese bronze, copper 83.45 per cent., manganese 13.48 per 
cent., iron 1.24 per cent., has a strength and ductility equal to that 
of open hearth steel, with 0.2 per cent, carbon. It is much used for 
marine propeller wheels because it does not corrode easily. 

The qualities of aluminum bronze have been experimentally 
investigated by Prof. L. von Tetmajer, of Zurich. The alloys used 
also contained silicon 1.18 per cent., and zinc 0.48 per cent. The 
range only extended from aluminum 5.5 per cent, to 11.5 per cent. 
The results are shown by the curves in Fig. 25. The full parts of 
the curves show actual results of experiments, the dotted parts being 
hypothetical. It will be seen that this alloy has great strength, 
combined with great ductility, from copper 91 to copper 95, and that 
this is the valuable range, as the ductility disappears at copper 89. 
The aluminum alloys are obtained by treating bauxite (a hydrated 
oxide of aluminum and iron), and copper in the Cowles electric 
furnace. 

All of the useful copper alloys are more or less forgable. “ Muntz 
metal,” copper 60, zinc 40, is rolled at a red heat into plates for 






















































































































































* 


. 





’ 



















































































































. 


















































ALLOYS. 


66 


sheathing ships, and into forms for holts and other fastenings. • It 
is stronger, cheaper, and more durable than pure copper. The 
effect of cold working upon the copper alloys is similar to that upon 
iron and steel : viz., the strength and hardness are increased, and 
the ductility is decreased, and hence the material is more brittle. 
This will be clear on comparing hard drawn brass wire with the 
same wire after annealing. 










CHAPTER VI. 


Selection of Materials. 

54.—The materials ordinarily used for machine parts are : 

(a) Crucible steel, sometimes called “ cast steel,” or “ tool steel.” 

(b) Bessemer, and open hearth steel, called also “machinery 
steel,” “soft steel,” “mild steel,” or “ingot iron.” 

(c) Wrought iron, also called malleable iron. 

(d) Cast iron. 

(e) Malleablized cast iron, also called malleable iron. 

(f) Steel castings. 

(g) Brass or bronze. 

(h) Babbitt metal. This name here includes all grades of white 
metal used for lining journal boxes, and bearings. 

Table of the qualities of materials which dictate their selection 


for machine 

parts : 




Material. 

Tensile 

Compressive 

Resilience or 
Shock 

Shaped lor 

Strength 

Strength. 

Resistance. 

use by 

(a) 

very high 

very high 

medium 

forging 

(b) 

high 

high 

high 

forging 

(0 

medium 

medium 

high 

forging 

(d) 

low 

very high 

low 

casting 

(e) 

medium 

— 

high 

casting 

(f) 

high 

high 

high 

casting 

(g) 

low 

— 

medium 

casting 
or forging 

(h) 

very low 

— 

— 

casting 


There should always be a film of oil between the metallic bearing 



SELECTION OF MATERIALS. 


68 


surfaces in machines, i.e., surfaces which rub together under pressure ; 
but for various reasons this film often fails temporarily, and the 
metal surfaces themselves come into contact. For this reason the 
material of bearing surfaces should be so selected that when, under 
exceptional circumstances they do come into actual contact, heating, 
and “cutting” of the surfaces shall not result. It is necessary, 
therefore, to know what metals will run together safely when lubri¬ 
cation is not perfect. 

Wrought iron or steel, either soft or hard, will run safely with 
wrought iron or steel, either soft or hard, and also with nearly all 
of the grades of brass and bronze, and babbitt metal. Wrought 
iron or steel on cast iron is to be avoided if the velocities and pres¬ 
sures are high and the failure of the lubricant possible. Cast iron 
upon cast iron runs very satisfactorily indeed. 

55.—To make clear the reasons which lead to the adoption of 
different materials for different machine parts, typical parts will be 
considered, and the reasons for the selection in each case will be 
given. 

The cylinder of a steam engine, with its ports, and its connected 
steam chest, is of so complicated form that it would be well nigh 
impossible to shape it by forging ; or if the forging were possible, it 
would be too expensive. The possible materials which may be 
used for such a cylinder are, therefore, only those which are shaped 
by casting. Brass and bronze would have no advantage over cast 
iron, and would cost about ten times as much. They are, therefore, 
out of the question. Steel casting might be used, but the first cost 
of the material would be somewhat greater, and the cost of work¬ 
ing in the machine shop would be very much greater. Additional 
strength and resilience would be gained, but this is unnecessary, 
as cylinders, even for very high pressures, can be made of cast iron, 
amply strong and resilient, and yet not objectionably thick. 
Moreover, cast iron is one of the very best possible materials for 
the wearing surfaces of the cylinder and valve seat. Cylinders sub¬ 
jected to excessively high pressure, as 300 to 700 pounds per square 
inch, would perhaps be better of steel casting ; as, for instance, the 











SELECTION OF MATERIALS. 


69 

cylinders of pumps for pipe lines, or for supplying hydraulic 
machinery. 

The piston rod of a steam engine is of soft steel. The entire 
force of the steam acting on the piston must he transmitted to the 
cross head through the piston rod ; also, since the effective area of 
the piston on the crank side equals the total area of the piston 
less the area of the rod, and since the effective area needs to he as 
large as possible, the rod should be as small as possible. There 
is always the liability to shocks, and therefore, since the rod must 
be small and at the same time strong, and must also he capable 
of resisting shocks, a material is required of high unit strength 
and of high resilience. Soft steel is the material which combines 
these qualities. 

A steam engine cross head pin is always made larger than is 
necessary to safely resist shearing, or springing by flexure, to in¬ 
sure the maintenance of lubrication ; cast iron might serve then, as 
far as strength and stiffness are concerned, and in fact is sometimes 
used. But there is another important consideration ; because of 
the vibratory motion of the connecting rod on the pin, there is a 
tendency to wear the pin oval, and then, when the boxes are 
“ keyed up,” they will bind when the rod is in its position of 
greatest angularity, if it is properly adjusted when the rod is on 
the centre line of the engine. Because of this it is desirable to re¬ 
duce the wear to a minimum, and this points to the selection of a 
hard material. Hardened tool steel might be used, but it is more 
expensive than soft steel or wrought iron, and there is the danger 
of hidden cracks, resulting from the hardening, which may. cause 
accident. If soft steel be case hardened, it will combine a hard surface 
to resist wear, with a soft resilient core, free from the danger of 
cracks. Wrought iron case hardened might be used, but wrought 
iron is not so good for a journal as soft steel, because, from the 
method of its manufacture, it has streaks of cinder in its surface, and 
lacks the homogeneity of the steel, and is therefore harder to make, 
and to keep truly cylindrical. It therefore should not he used 
where perfection of bearing and accuracy of movement are essential. 






SELECTION OF MATERIALS. 


70 


The connecting rod of a steam engine is subjected to the alternate 
tension and compression resulting from the pressure on the 
piston, and also to a flexure stress due to its vibratory motion. 
These stresses are very severe, and there is also liability to 
shock. The material of the rod should be strong and resilient, and 
soft steel would naturally be selected, since it is a forgable material. 
But there is another important consideration. The rod is to be 
finished, and wrought iron is much more cheaply worked in the 
machine shop than soft steel, and the expense of forging is also 
much less. The lack of homogeneity is of no importance, as no part 
of the rod is a bearing surface. Many connecting rods are made of 
steel casting, and finished by painting. This makes a cheaper rod, 
but there is always the danger of hidden defects, like cracks, due to 
the excessive shrinkage, or “ blow holes,” which may weaken the rod 
enough to cause accident. 

The cross head of a steam engine is composed of two parts : (a) 
that which serves to transmit the pressure from the piston rod to 
the cross head pin, and (b) that which engages with the guide to 
produce rectilinear motion parallel to that of the piston. The 
stresses on (a) are severe, and it is also liable to severe shock, and 
hence it must be of strong resilient material ; the stresses on (b), 
however, are not very great, but it must be of material which will 
run well with the guide, which is usually of cast iron, being a part 
of the engine bed. The cross head may he made of materials as 
follows : (a) may be made of forged wrought iron, or soft steel, and 
(b) may be of cast iron bolted to (a), or the whole cross head may 
be made of cast iron, the part (a) being made enough larger than 
before to lie sufficiently strong; or the cross head may be made a 
casting of steel and a “shoe” or “gib” of cast iron or brass may be 
added to provide a proper surface to run in contact with the guide. 

The crank pin of a steam engine is subjected to the same stress 
as the cross head pin, and the velocity of rubbing surface is very 
much greater, hence the tendency to wear is greater. The wear in 
this case, however, tends to keep the pin approximately round, and 
therefore does not interfere with the correct adjustment of the boxes ; 



s 




SELECTION OF MATERIALS. 


71 


hence there is not so great necessity for keeping the wear a minimum 
value ; a good journal surface is necessary, and soft steel is used 
without case hardening. 

The main shaft of a steam engine needs to be strong and rigid to 
resist a combination of severe stresses, the torsional and trans¬ 
verse stress from the connecting rod, and the transverse stress due to 
the weight of the fly-wheel, and the belt tension. It must also afford 
a good journal surface, and for these reasons it is made of soft steel. 

The function of the fly-wheel of a steam engine is to adapt a 
varying effort to a constant resistance, and it does this by absorb¬ 
ing and giving out energy periodically by virtue of its inertia, 
which is proportional to its weight; it therefore needs, above all 
things, to be heavy ; it also needs to be able to resist the bursting 
tendency of the centrifugal force due to its rotation. The most 
suitable material is therefore that which gives the greatest weight 
in the required form, with the required strength, for the least money ; 
and cast iron best fulfils these requirements. 

An engine bed or frame, when it is in one piece, is of cast iron, 
and the reasons are obvious ; its form is complex, and could only 
be produced by casting ; weight is not objectionable, but rather an 
advantage, since it absorbs vibrations ; cast iron is amply strong, 
and affords good wearing surfaces for the cross head guides. 
Wrought iron is used for engine beds where vibrations are of no 
importance, as in the locomotive, and where lightness and compact¬ 
ness are very desirable, as in some marine engines. The beds of 
some of the large roll train and blowing engines are built up of 
wrought and cast iron. 

The journal bearings, or boxes for the cross head pin, the crank 
pin, and the journals of the main shaft, are usually made now of 
cast iron or brass, with a babbitt metal lining, because, first, good 
babbitt metal (tin 80, copper 10, antimony 10) is found to be a 
better bearing metal than brass, i.e., it runs with less tendency to 
heat; and second, in the case of the cutting out of the surface, the 
babbitt lined box is far more quickly and cheaply renewed than the 
solid brass box. 



SELECTION OF MATERIALS. 


72 


The eccentric and its strap are almost invariably made of cast 
iron, because they are forms which are forged with difficulty, and 
the cast iron affords ample strength and excellent wearing surfaces. 
The eccentric rod, on the other hand, would be cumbersome and 
ugly in appearance if it were made of cast iron, and given sufficient 
strength. It is a form which may be easily either forged or cast, 
and is made of forged wrought iron or steel, or of cast steel, or of 
malleablized cast iron. Rocker arms also, when they are used, 
require to be of a resilient material, and when of simple form may 
be forged of wrought iron or steel ; and when of more complex form, 
may be of malleablized cast iron, or steel casting. The valve is 
usually of somewhat complex form, and needs to wear well with the 
cast iron valve seat, and so is almost invariably of cast iron. 

56.—Considerations similar to those above apply to the selection 
of proper material for the parts of machine tools. Thus, in the case 
of a lathe, the bed, legs, head and tail stock, cone, gears, etc., are of 
cast iron, because they are all forms which are most cheaply and 
satisfactorily produced by casting, and the cast iron affords the 
required strength and stiffness, and satisfactory wearing surface, 
where they are required. Such parts as lead screws, feed rods, and 
other parts which are subjected to some considerable stress, and 
have great length relatively to their lateral dimensions, are made 
necessarily of wrought iron or steel. Many of these parts may be 
finished in the machine shop, directly from merchant bar stock, and 
the expense of forging may be saved. 

The material for the parts of planing, milling, and drilling 
machines are determined from exactly similar considerations. 

Spindles, however, require special attention. In lathes, milling 
and grinding machines, the accuracy of the work produced depends 
largely upon the accuracy of the spindle. 

The vital point is therefore to maintain this accuracy, i.e., to 
prevent wear as far as possible. It would seem then that hardened 
tool steel would be the best material.* But since only a very small 
amount of stock can be removed by the grinding machine after the 
piece is hardened, the spindle must be roughed out very nearly to 




SELECTION OF MATERIALS.. 


73 


size before it is hardened ; this involves a very considerable expense, 
and there is danger that it may crack in hardening, or spring so as 
not to hold up to finish, in which case the loss it great, and it is 
found that the risk cannot be taken. The next best thing is to 
specify machinery steel high in carbon (say 0.4 per cent.), and to 
use this harder material for the spindle without hardening. In 
milling machines, and in some lathes, the main spindle box is solid, 
of tool steel, hardened and ground (the risk of loss being less in this 
case), and the spindle as before is of 0.4 per cent, carbon machinery 
steel. The wear is thus greatly reduced, and the possibility of wear 
after long use is provided against by making the bearing taper, and 
providing end adjustment. The spindles of very large lathes are 
made of cast iron, because forged material would be too expensive. 
The wear is reduced by making the journals very large. 

In the steam or hydraulic riveter, the main frame which sup¬ 
ports the cylinder, and carries the guide for the moving die, may be 
of any reasonable size, and therefore can be made strong enough to 
resist even the very great stresses which come upon it, if the 
material used is cast iron. But the “ stake,” the member which 
carries the stationary die, must resist exactly the same stresses 
which come upon the main frame, and must also be small enough 
so that small boiler shells, and even flues can be lowered over it to 
be riveted. The “stake” is therefore of forged wrought iron or 
steel, or else a steel casting. 

Suppose that in a machine there is need of a gear and pinion 
whose velocity ratio is 8 to 1, and that the force transmitted is large. 
A tooth of the pinion conies'into action eight times as often as a 
tooth of the gear, and therefore would wear out in one eighth of the 
time, if both were of the same material; then, too, the form of the 
pinion tooth in most systems of gearing is such that it is much 
weaker then the gear tooth. The material for the pinion needs, 
therefore, not only to be stronger, but also better able to resist wear. 
The gear is made of cast iron ; if the teeth are cut, the pinion may 
be made of forged steel ; if the teeth are cast* and used without 
“ tooling,” the pinion may be made a steel casting. 

10 



Average Values of Strength of Materials. 


selection of materials. 




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B I BLIOGRAPHY. 


The following bibliography is given as a help to collateral 
reading. The books and papers are numbered, and reference is 
made to them *by number under the subjects given. 

1. American Foundry Practice, 1 vol., by Thos. D. West. John Wiley & 

Sons, New York. 

2. An Introduction to the Study of Metallurgy, 1 vol., by W. C. Roberts- 

Austen. J. B. Lippincott, Philadelphia. 

3. A Text Book of the Materials of Construction, 1 vol., by R. H. Thurs¬ 

ton. John Wiley & Sons, New York. 

4. Applied Mechanics, 1 vol., by Gaetano Lanza. John Wiley & Sons, 

New York. 

5. A Treatise on the Metallurgy of Iron, 1 vol., by H. Bauerman. Crosby 

Lockwood & Son, London. 

6. Jpurnal Iron and Steel Institute, 1886, Vol. I., p. 174. T. Turner. 

7. Mechanics of Engineering, 1 vol., by I. P. Church. John Wiley & 

Sons, New York. 

8. Mechanics of Materials, 1 vol., by Mansfield Merriman. John Wiley 

& Sons, New York. 

9. Metallic Alloys, 1 vol., by William T. Brannt. Henry Carey Baird & 

Co., Philadelphia. 

10. Metals, 1 vol., by Bloxam and Huntington. Text Books of Science 

Series, D. Appleton & Co., New York. 

11. The Elasticity and Resistance of the Materials of Engineering, 1 vol., 

by Wm. H. Burr. John Wiley & Sons, New York. 

12. The Management of Steel, 1 vol., by George Ede. William Tweedie, 

337 Strand, London. 

13. The Metallurgy of Steel, 1 vol.,-by H. M. Howe. Scientific Publishing 

Co., New York. 







BIBLIOGRAPHY. 


76 


14. The Testing of Materials, 1 vol., by W. C. Unwin. Longmans, Green 

& Co., New York. 

15. Trans. Am. Inst. Mining Engineers, Vol. XVIII., p. 102. J. W. Keep. 

16. Steel and Iron, 1 vol., by W. H. Greenwood. Manuals of Technology, 

Cassell & Co., New York. 

17. Steel Car Axles, Trans. Am. Soc. Mechanical Engineers, Vol. IX., p. 

135. John Coffin. 

18. Steel, Its Properties, etc., Trans. Am. Soc. Civil Engineers, Vol. XV., 

p.283. William Metcalf; discussion by John Coffin. 

19. Wedding’s Basic Bessemer Process, 1 vol., Translated by Phillips and 

Prochaska. Scientific Publishing Co., New York. 


Subjects and References. 


Alloys, 2, 3, 9, 14, 15. 

Basic Bessemer process, 10, 19. 

Bessemer process, 3, 5, 10, 13, 16. 

Blast furnace, 3, 5, 10, 16. 

Chemical changes, for detailed study 
of see Chemical Phenomena of Iron 
Smelting, by I. Lowthian Bell. 
Also his papers in Journal of Iron 
and Steel Inst, and Am. Inst. Min¬ 
ing Engineers. 

Cast iron, 1, 3, 5, 6, 10, 14, 15, 16. 

Combustion, 10. 


: Foreign substances, effect of on iron, 
2, 3, 6, 9, 10, 13, 15, 17, 18. 

Fuels, 2, 5, 10. # 

Furnaces, 2, 5, 10, 13, 16. 

Heat treatment of steel, 2, 3, 12, 13, 
17, 18. 

i Ores, 5, 10, 16. 

Puddling, 3, 5, 10, 16. 

Repeated stress, effect of, 3, 4, 8, 14. 
Steel, 3, 5, 10, 12, 13,16, 17, 18. 
Testing of materials, 3, 4, 7, 8, 11, 14. 
Wrought iron, 3, 5, 10, 14, 16. 












•, 






































, f 

. * 


















. * 































. 







* f , 


• . * 











































. 























































































I N DEX. 


After blow, basic process, 21. 

Air, amount used per pound of car¬ 
bon burned, 2. 
furnace, 24. 

required for combustion of CO, 5. 
Alloys, 62. 

Aluminum, effect of on steel, 54. 

in varying amounts, effects on 
copper, 65. 
bronze, 64. 

bronze, experiments on by Prof. 
L. von Tetmajer, 65. 

Annealing, methods, 50. 
objects of, 50. 
of steel castings, 49. 

Anthracite coal, 3. 

Antifrictional qualities, 68. 

Basic Bessemer process, 20. 
Bauschinger on repeated stress, 57. 
Bed of steam engine, material for, 71. 
Bessemer converter, 18. 
process, 18. 

steel, composition of, 18. 
Bituminous coal, 3. 

Blackband ore, 10. 

Blast furnace, 11. 

Blister steel, 18. 

Bloom, 16. 

“ Blue heat,” 50. 


Bog ores, 10. 

“ Boshes,” 12. 

Brass, 62. 

Bronze, 62. 

aluminum, 64. 
manganese, 64. 
phosphor, 64. 

Burnt scrap, 39. 

Calcining iron ore, 10. 

Calorific intensity, definition, 2. 
of carbon, 3. 
of carbonic oxide, CO, 4. 
of hydrogen, 5. 

Calorific power, definition, 2. 
of carbon, 4. 
of carbonic oxide, CO, 4. 
of hydrogen, 5. 

Car axles, process for toughening, 49. 
Carbon, calorific intensity of, 3. 
calorific power of, 4. 
hardening, 46. 

• in cast iron, 32. 

in cast iron, control of the dis¬ 
tribution of, 34. 

in steel, as affected by heat treat¬ 
ment, 46. 

non-hardening, 46. 

< reduction of by melting cast iron 
with burnt scrap, 39. 







INDEX. 


78 


Carbonic oxide, calorific intensity of, 
4. 

calorific power of, 4. 

Case hardening, 52. 

Castings, ductile, 23. 
fillets in, 41. 

for different purposes, 36. 
forms of, to avoid shrinkage 
stresses, 42. 
lessons in design of, 42. 
round corners in, 41. 

Cast iron, carbon in, 32. 
effect of remelting, 38. 
foreign substances in, 31. 
grades, 32. 

influenced by combined and gra¬ 
phitic carbon, 33. 
spongy sections in, 41. 
strength of, 33. 

Cellulose, composition, 3. 
Cementation process, 17. 

Charcoal, 4. 

Charge, blast furnace, materials of, 

12 . 

Chemical reactions in the blast fur¬ 
nace, 12. 

Chilling of cast iron, 34. 

Chromium, effect on steel, 54. 

Clay ironstone, 10. 

Coals, constituents of, 4. 

Coffin’s toughening process for car 
axles, 49. 

Coke, 4. 

Cold rolling, effect of on physical 
qualities, 56. 

Cold working, effect of on alloys, 66. 
Combined carbon, influence of on 
cast iron, 33. 

Combustion, complete, 1. 
of CO, 4. 

Comparison of materials by stress- 
strain diagram, 29. 


Connecting rod of steam engine, ma¬ 
terial for, 70. 

Converter, Bessemer, 18. 

lining in acid Bessemer process, 

20 . 

lining in basic Bessemer process, 

20 . 

Cooling, effect of on cast iron, 40. 
rate of, effect on cast iron, 34. 

Copper and tin, 62. 
and zinc, 62. 

as affected by varying amounts 
of aluminum, 65. 
as affected by varying amounts 
of tin, 62. 

as affected by varying amounts 
of zinc, 63. 
tin, and zinc, 62. 
tin, and zinc in varying amounts, 
effect of mixing, 64. 

Cowper hot blast stove, 14. 

Crank pin of steam engine, material 
for, 70. 

Cross head of steam engine, material 
for, 70. 

Cross head pin of steam engine, ma¬ 
terial for, 69. 

Crucible process, 18. 

steel ingots, mechanical treat¬ 
ment of, 18. 

Crystallization (so called) from re¬ 
peated stress or shock, 61. 

Cupola, foundry, 9. 

Cylinder of steam engine, material 
for, 68. 

Dilution, reduction of carbon by, 
24. ' 

Direct process of iron smelting, 11. 

Dissociation of CO and C0 2 , 8. 

Dry puddling, 16. 

Ductility, 28. 





INDEX. 


79 


Early methods of iron production, 11. 
Eccentric and strap of steam engine, 
material for, 72. 

rod of steam engine, material for, 
72. 

Elasticity, definition of, 26. 

Elastic limit, definition, 26. 

effect of stress exceeding, 55. 
Elastic strain, definition, 27. 

Factors of safety, 59. 

reasons for use, 59. 
Ferro-aluminum, 23. 
Ferro-manganese, 20. 

Ferro-silicon, 23. 

Fillets in castings, 41. 

Fluid shrinkage of cast iron, 40. 

Flux, 11, 12. 

Fly wheel of steam engine, material 
for, 71. 

Foreign substances, effect of upon in¬ 
got iron or steel, 52. 

Forged materials, internal stresses 
in, 45. 

variation in physical qualities of, 
45. 

Foundry, variety of product required 
from, 36. 
cupola, 9. 

Frame of steam engine, material for, 
71. 

Franklinite iron ore, 10. 

Fuels, 1. 

artificial, 3. 
classified, 3. 
gaseous, 5. 
raw, 3. 

Furnaces, air, 24. 
classification, 8. 
reverberatory, 9. 

Ganister, 18, 20. 


Gas, generator, production of, 6. 
generator, composition of, 7. 
illuminating, composition of, 6. 
illuminating, production of, 6. 
water*, composition of, 6. 
water, production of, 6. 

Gases, waste, from blast furnace, 
composition of, 13. 

Gaseous fuel, 5. 

advantages of, 5. 

Generator gas, composition of, 7. 
production of, 6, 

Siemens, 6. 

Grades of cast iron, 32. 

Graphitic carbon in cast iron, 32. 
influence of on cast iron, 33. 

Haematite iron ores, 10. 

Hardening steel, 51. 
precautions, 51. 

Heat treatment, effect on carbon dis¬ 
tribution in steel, 46. 
effect upon structure of wrought 
iron and steel, 46. 

Homogeneousness, effect of lack of on 
stress-strain diagram, 45. 

Hooke’s law, 26. 

Hot blast, 14. 

Hot blast stoves, cast iron, 14. 

Cow per, 14. 

Whitwell, 14. 

Hydrogen, calorific intensity of, 5. 
calorific power of, 5. 

Illuminating gas, composition of, 6. 
production of, 6. 

Ingot iron, 25. 

• steel, 25. 

Internal stress, effect on the stress- 
strain diagram, 43. 
in forged materials, 45. 
relieved by annealing, 50. 






INDEX. 


80 


Iron carbonate, 10. 

Iron, cast, foreign substances in, 31. 
ingot, 25. 
ores of, 9. 
sources of, 9. 
weld, 25. 

wrought, foreign substances in, 
31. 

Journal boxes of steam engine, ma¬ 
terial for, 71. 

Kalchoids, 62. 

Lignite, 3. 

Lime in the basic Bessemer process, 

21 . 

Machine tools, materials for, 72. 
Magnetic iron ore, 9. 

Main shaft of steam engine, material 
for, 71. 

Malleable castings, 23. 
Mal-treatment, effect of, 55, 
Manganese bronze, 64. 

Manganese, effect upon steel, 53. 

for controlling the distribution of 
carbon in cast iron, 35. 
Materials classified for selection, 67. 
compared by stress-strain dia¬ 
gram, 29. 
testing of, 26. 

Maximum stress, definition of, 27. 
Mechanical working, effect of on 
structure, 49. 

Merchant bar, 16. 

Muck bar, 16. 

Muntz metal, 65. 

Nickel, effect of on steel, 54. 
Nomenclature of iron and steel, 24. 


Open hearth process, 22. 

Ores, impurities in, 10. 
of iron, 9. 

Oxidation in the puddling process, 16. 
Oxidizing agents in the puddling pro¬ 
cess, 16. 

Phosphor bronze, 64. 

Phosphorus, effect of on the distribu¬ 
tion of carbon in cast iron, 35. 
effect upon steel, 53. 
limit of in cast iron, 35. 
removal of in puddling, 17. 
removal of in the basic Bessemer 
process, 20. 

Physical qualities as affected by mal¬ 
treatment, 55. 

as affected by repeated stress, 57. 
as affected by straining past elas¬ 
tic limit, 55. 

of forged materials, variations, 
causes, and control, 45. 
of cast iron, 31. 

Pig and ore process, 22. 

and scrap process, 22. 

Pig iron, composition of, 12, 15. 

for basic Bessemer process, com¬ 
position, 2i. 
uses made of, 15. 

Piston rod of steam engine, material 
for, 69. 

Puddle ball, 16. 

Puddling process, 15. 

Rate of cooling of cast iron, effect of, 
34. 

Reactions in iron ore reduction, 11. 
Red haematite iron ore, 10. 
Regenerative furnace, Siemens, 8. 
Refinery, 17. 

Refining, 17. 

Reverberatory furnace, 9. 




INDEX. 


81 


Remelting cast iron, effect of, 38. 
Resilience, 28. 

Roasting iron ore, 10. 

Rocker arms for steam engine, mater¬ 
ial for, 72. 

Round corners in castings, 41. 

Scotch pig, 39.; 

Scrap, nse of in foundry, 38. 

Selection of materials, 07. 

Set, definition of, 27. 

Shrinkage stress in castings, 42. 
Shrinkage in .steel castings, 24. 
of cast iron, 36, 40. 
fluid, of cast iron, 40. 

' solid, of cast iron, 40. 

of cast iron, West’s experiment, 
41. 

Side-rite iron ore, 10. 

Siemens gas generator, 6. 
process, 22. 

-Martin process, 22. 
regenerative furnace, 8. 

Silicon, effect of on the strength of 
cast iron, 37. 
effect upon steel, 52. 
for controlling the distribution 
of carbon in cast iron, 35. 
reduction of by melting with 
burnt scrap, 39. 

Slag, 11. 

blast furnace, composition of, 

12 . 

from basic Bessemer process, 

- 21 . 

from puddling process, 16. 
Softening scrap, 39. 

Solid shrinkage of cast iron,.40. 
Spathic ore, 10. 

Spiegel-eisen, 10, 20. 

Spindles, material for, 72. 

Spongy sections in cast iron, 41. 


Steel as affected by aluminum, 54. 
as affected by chromium, 54. 
as affected by manganese, 53. 
as affected by nickel, 54. 
as affected by phosphorus, 53. 
as affected by silicon, 52. 
as affected by sulphur, 53. 
as affected by tungsten, 51. 
castings, 23. 

castings, annealing of, 49. 
hardening of, 51. 
ingot, 25. 
tempering of, 51. 
tendency to crack in hardening, 
51. 

weld, 25. 

Stiffness, 28. 

Strain, definition of, 26. 
elastic, definition of, 27. 
permanent, definition of, 27. 
Strength as affected by internal 
stresses, 43. 

as affected by lack of liomogene- 
ousness, 46. 

as affected by mal-treatment, 55. 
at elastic limit, 28. 
of cast iron as affected by silicon, 
36. 

of steel as affected by heat treat¬ 
ment, 46. 

ultimate, definition of, 27. 

Stress, definition of, 26. 

introduced by shrinkage, 42. 
maximum, definition of, 27. 
repeated, effects of, 27. 
Stress-strain diagram, 27. 

as affected by lack of homogene¬ 
ousness, 45. 

.effect of internal stresses on, 43. 
of brittle material, 27. 
of ductile material, 27. 

Stress, unit, definition of, 27. 






INt>EX. 


82 


Structure as affected by mechanical 
working, 49. 

of steel as affected by heat treat¬ 
ment, 46. 

Sulphur, effect of on the distribution 
of carbon in cast iron, 35. 
effect Upon steel, 53. 
limit of in cast iron, 35. 
removal of in puddling, 17 

Temperature in the Bessemer con¬ 
verter, control of, 21. 

Tempering steel, 51. 

Testing of materials, 26. 

Thermal unit, British, definition, 2. 

Tin, copper, and zinc in varying 
amounts, effects of mixing, 64. 
in varying amount, effect of on 
copper, 62. 

•Tool steel, carbon in, 17. 

from wrought iron, processes for 
making, 17. 

Tungsten, effect of on steel, 54. 

Turner’s experiments on silicon in 
cast iron, 35. 


Tuyeres, blast furnace, 12. 

Unit stress, definition, 27. 

Variety of product required from 
foundry, 36. 

Water gas, composition of, 6. 

production of, 6. 

Weld iron, 25. 
steel, 25. 

Wet puddling, 16 
Wheels, cast, design of, 42 
Whitwell hot blast stoves, 14 
Wire drawing, effect of on physical 
qualities, 57. 

Wohler’s law, 57. 

Wood, for fuel, 3 
Wrought iron, composition of, 15 
foreign substances in, 31. 

Zinc, copper, and tin in varying 
amounts, effect of mixing, 64. 
in varying amount, effect of on 
copper, 63. 





THE 



onstructive 


Materials 


OF 


ENGINEERING 


/ 
w 

A* 


Albert W. Smith 


Professor of Mechanical Engineering, Leland Stanford Junior Lniversity 



Palo Alto Press: 

Leland Stanford Junior University 
1892 











































# 



















































































